Communication module

ABSTRACT

A communication module comprises a substantially token-shaped body with first and second electrically conductive surface areas. The first and second surface areas are electrically isolated from each other and circuitry is positioned in the cavity within the substantially token-shaped body, and has connections to said first and second areas. The substantially token-shaped body has a perimeter around it. The first and second electrically conductive surface areas form a substantial portion of the substantially token-shaped body. The first and second electrically conductive surface areas form a cavity. One of the surface areas forming a flange around the perimeter of the substantially token-shaped body. The flange preferably resides in one geometric plane. The circuitry provides for the receipt and transmission of digital signals that are determined as voltage differences between said first and second areas. The circuitry preferably includes a capacitor for storing energy from said voltage intermittently applied between the first and second areas, so that the circuit is powered by a battery within said body. The first area comprises one flat face of the body and the second area comprises a second flat face parallel to said one flat face plus a portion of a curved surface which is perpendicular to said flat faces. The circuitry includes (1) a voltage level detector coupled to the first and second areas for receiving signals applied as voltage differences between the first and second areas and (2) a switch connecting the first and second areas for sending signals by changing the resistance between the first and second areas. The voltage level detector preferably detects only two levels.

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All of the material in this patent application is subject to copyrightprotection under the copyright laws of the United States and of othercountries. As of the first effective filing date of the presentapplication, this material is protected as unpublished material.

Portions of the material in the specification and drawings of thispatent application are also subject to protection under the maskworkregistration laws of the United States and of other countries.

However, permission to copy this material is hereby granted to theextent that the copyright owner has no objection to the facsimilereproduction by anyone of the patent document or patent disclosure, asit appears in the United States Patent and Trademark Office patent fileor records, but otherwise reserves all copyright rights whatsoever.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 998,978,filed Dec. 30, 1992, now abandoned, which is a divisional of Ser. No.07/725,793 filed Jul. 9, 1991, now abandoned; which is a CIP ofPCT/US90/02891 filed May 15, 1990, which is a CIP of Ser. No. 07/615,606filed Nov. 19, 1990, now U.S. Pat. No. 5,206,905, which is a CIP of Ser.No. 07/615,615 filed Nov. 19, 1990, now abandoned which is a CIP of Ser.No. 07/615,608 filed Nov. 19, 1990, now U.S. Pat. No. 5,226,139, whichis a CIP of Ser. No. 07/615,618 filed Nov. 19, 1990, now abandoned whichis a CIP of PCT/US91/03376 filed May 15, 1991.

This application is a continuation-in-part of the following applicationsof common assignee, all of which are hereby incorporated by reference:Ser. No. 07/725,793, filed Jul. 9, 1991, "Memory" (DSC-175);PCT/US90/02891, filed May 15, 1990, "Systems withData-Token/One-Wire-Bus" (DSC-83PCT); Ser. No. 615,606, filed Nov. 19,1990, "Electronic Key with Repeatable False Responses" (DSC-303); Ser.No. 615,615, filed Nov. 19, 1990, "Low-Power Memory with Block MovesImplemented by Pointer Update" (DSC-304); Ser. No. 615,608, filed Nov.19, 1990, "Electronic Key with Multiple Subkeys Writable Via Scratchpad"(DSC-305); Ser. No. 615,618, filed Nov. 19, 1990, "Low-Power IntegratedCircuit with Selectable Battery Modes" (DSC-306); Ser. No. 631,929,filed Dec. 19, 1990, "Printer Port Adapter with Overlaid One-WireInterface for Electronic Key" (DSC-316); and Ser. No. PCT/US91/03376,filed May 15, 1991, "Electronic Key Integrated Circuit" (DSC-303PCT).

The following applications of common assignee contain related subjectmatter and are believed to have an effective filing date identical withthat of the present application:

Ser. No. 07/728,230, filed Jul. 10, 1991, entitled "Power HistoryMonitor Chip" (DSC-317), now abandoned;

Ser. No. 07/727,618, filed Jul. 10, 1991, entitled "IntegratedCounter/RAM Array Layout" (DSC-319), now abandoned;

Ser. No. 07/727,619, filed Jul. 10, 1991, entitled "Timekeeping Chipwith Clock-to-Memory Update Only on Read Signal" (DSC-322), nowabandoned;

Ser. No 07/727,638, filed Jul. 10, 1991, entitled "Integrated Circuitwith Scratchpad Copy to Any Portion of a Page" (DSC-324), now abandoned;

Ser. No. 08/103,724, filed Aug. 9, 1991, entitled "Electronic Key withThree Modes of Automatic Self-Disablement" (DSC-352);

Ser. No. 07/727,639, filed Jul. 10, 1991, entitled "Integrated Circuitwith Both Battery-Powered and Signal-Line-Powered Areas" (DSC-353) nowU.S. Pat. No. 5,166,545;

Ser. No. 07/728,229, filed Jul. 10, 1991, entitled "Level-ShifterCircuit for Crossing Power-Supply-Domain Boundaries" (DSC-354), nowabandoned;

Ser. No. 07/727,270, filed Jul. 10, 1991, entitled "Socket with SolderOption from Internal One-Wire Bus to Female Pin" (DSC-355), nowabandoned;

and Ser. No. 07/727,273, filed Jul. 10, 1991, entitled "Power-On-ResetCircuit" (DSC-356), now U.S. Pat. No. 5,166,545.

These applications are hereby incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to compact electronic modules, and tocomponents and packaging for use with such modules.

One of the long-term trends in electronics has been to provide higherfunctionality at lower cost in a more compact package. Many pages havebeen written on this long-term trend, and it will not be analyzed here.However, the numerous innovations disclosed in the present applicationare believed to contribute to a major advance in this direction.

Module

The present application discloses a very compact electronic module,which includes an integrated circuit (preferably including memory) and abattery. The module is preferably coin-shaped, and the two faces of themodule are isolated from each other. Host systems can read/write accesssuch modules, by using a one-wire-bus protocol.

One-Wire-to-Three-Wire Converter

The module may contain one integrated circuit or several, but theintegrated circuits in the module preferably include aone-wire-to-three-wire converter circuit. In the presently preferredembodiment, this is integrated on a single chip with a small amount ofserial-access memory. However, alternatively the converter may be usedto provide a standard three-wire serial bus output, which provides aninterface to one or more other chips. The other chips may include, forexample, electronic keys (such as the DS1207 from Dallas Semiconductor).

ESD Protection Needs

A common specification for integrated circuits is the ability towithstand five successive electrostatic discharges (ESD's) each of 1000Volts without the leakage current increasing to 1 microampere. However,a de facto standard of 2000 V ESD immunity has been springing up formany applications.

However, even this level of ESD immunity maybe insufficient forhigh-noise applications. Specifically, in the large-scale systemsenvironment of the presently preferred embodiment, the data modules willface some unusual integrity requirements. Since the modules may beexposed to very rough treatment, in consumer and industrialenvironments, they should preferably have a very high level of immunityto electrostatic discharge (ESD).

The electronic data module of the presently preferred embodimentincludes an ESD protection diode structure, which helps to protectagainst data loss under severe electrostatic discharge conditions.

Packaging Scheme

To fit the integrated circuit into this very small space, a packagingscheme is used in the preferred embodiment. A two-part metal containeris used, which has two shallow concave pieces which fit together. Theintegrated circuit (preferably in a low-height package, such as aflat-pack or small outline integrated circuit (SOIC) is mounted on avery small printed circuit board (preferably a flexible board), whichfits inside the container. Laterally spaced from the integrated circuit,on the other end of the small board, the board end is sandwiched betweena battery and a piece of elastic conductive material (such as conductiveplastic foam). Thus, the battery is connected between one face of thecontainer and a power conductor on the board. The piece of elasticconductive material makes contact between a data trace on the board andthe other face of the container. Another trace on the board makescontact directly to the container face on which the battery's groundterminal is connected. Thus, simple wiring on the small board, usingthrough-hole vias, suffices to route power, ground, and data lines tothe integrated circuit, while providing a sealed durable package withtwo external contacts.

The battery is preferably a low-voltage battery (1.5 V, in the preferredembodiment.) This is cheaper, and maximizes power efficiency, butrequires some circuit design features to accommodate the electricalinterface. (Electronic watches have often been powered by 1.5 Vbatteries, but such devices do not have any direct electrical interfaceto the outside world. By contrast, the module of the presently preferredembodiment communicates over a one-wire bus which is driven by full CMOSvoltage levels.)

Module Mounting and Adhesion

The electronic token modules can be used in several ways. For example,in some embodiments it may be preferable to use loose tokens. However,in many applications (such as inventory control, machinery maintenancerecords, or retail tagging) it may be preferable to mount the tokens onthe physical items to which the data in the individual tokens refers. Inthis case, the token must be mounted so that both terminals of the tokencan be contacted by the user. In the presently preferred embodiment(using a package like that shown in FIG. 1A), only one of the possibleorientations will work. (The inner casing piece 100A must be exposed,and therefore, if the token is to be mounted on a surface, it is theouter casing piece 100B which should be adhered to the surface.)

For such applications, the packaged modules (in embodiments usingpackages like those of FIGS. 1A and 1B) are preferably shipped withdouble-sided adhesive tape already affixed to the side of the modulewhich is to be adhered to a surface (face 100B, in the example of FIG.1B).

Integrated Circuit

The module, in the presently preferred embodiment, contains anintegrated circuit which itself includes several features. Thisintegrated circuit, in the presently preferred embodiment, includes anelectrical interface to the one-wire bus (including heavy protectionagainst minority carrier injection), a one-wire-to-three-wire convertercircuit, and a small amount of serial-access memory.

The integrated circuit, in the preferred embodiment, contains 256 bitsof serial-access memory. This memory is read- or write-accessed as asingle block transfer. It is contemplated that larger amounts of memorymay be advantageous. Of course, other types of memory organization canbe used instead; but for many applications it is contemplated that useof a very small amount of memory (4K or less) may be particularlyadvantageous, since this extends the battery lifetime.

Low-Voltage SRAM Architecture

Among the teachings set forth in the present application is a low-powerlow-voltage Complementary Metal Oxide Semiconductor (CMOS)six-transistor static random access memory (SRAM), which can operate ona power supply voltage which is less than the sum of the 7-channel MOS(NMOS) and p-channel MOS (PMOS) threshold voltages, and which does notinclude any analog or metastable sense amplifier stages. The selectedcell is allowed to pull one of its bitline pair all the way down toground. Thus, full logic levels appear on the bitline pair. Only oneline of the bitline pair is connected to the following gate stage.Preferably bitline precharge transistors are connected to pull up allbitline pairs whenever the RAM is not selected.

RAM/ROM Hybrid Memory

A further teaching, in the preferred embodiment, is the use of RAM/ROMhybrid for a portion of the memory array. An memory cell is used, whichcan operate as a static RAM, or which can be programmed to operate as aread only memory (ROM) cell. Thus users who need the extra securitypermitted by ROM encoding can have this capability, while users who donot need ROM encoding can use off-the-shelf parts as RAM only.

Chip Series with Unique Hard-wired Identifications

A further large-scale system concept is to use the capability tointroduce ROM into the memory space to provide memory chips withcompletely unique hard-wired identifications. This provides tremendousadvantages for security-related needs.

In this embodiment, an external system can test the chip's integrity, byperforming a read-write-read operation on the memory space which issupposed to be ROM, and also on a portion of the memory space which isexpected to be RAM. This will provide at least some insurance againstthe ROM identification being emulated in RAM. Optionally, the externalsystem can even test the data output timing, to ascertain whether theRAM and ROM outputs are timed identically (and therefore to assure thatthe address inputs are not being decoded to address two differentchips).

This also provides advantages of failure protection. Very fewcatastrophes will be able to eradicate the hardware encoding of thecells which have been converted to ROM. (Even if the electricalfunctionality is totally destroyed, the fuse pattern can be readoptically.) Thus, recovery of these bits may provide useful informationin failure analysis. (For example, a manufacturing lot number can becross-referenced from a unique identification number in ROM. This wouldprovide greatly enhanced capabilities for analysis of late failures.

For another example, where the nonvolatility is electricallyprogrammable, a system which recognized an imminent catastrophic failure(e.g. an avionics system facing a crash) might be able to save some datain the memory at the last minute.

ESD Protection Diode

The presently preferred embodiment uses an protection diode structure,in which a significant device-level feature, is the provision of anintermediate-depth diffusion. This intermediate-depth diffusion willhave a junction depth (inside the P-well or N-well) which issignificantly deeper than the source/drain junction depth, butsignificantly shallower than the depth of the well. Thisintermediate-depth diffusion is useful in the diode structure described,but can also be used for other device structures. For example, thisstructure provides a compact bipolar transistor structure withreasonably high gain. This intermediate-depth diffusion can also be usedfor input protection structures (i.e. to provide device structures whichwill rapidly and recoverably break down, when a high-voltage pulseappears, to discharge the high-voltage pulse without damaging theprimary circuitry of the chip). For another example, thisintermediate-depth diffusion can also be used to form diffusedcapacitors with relatively large capacitance per unit area, orcapacitors whose capacitance varies greatly with voltage (suchcapacitors are commonly referred to as varactors.)

A further advantage of this structure, and a further teaching set forthherein, is that the structure can be fabricated with minimal addedprocess complexity. An intermediate-depth diffusion is added to astandard process flow; but the shallow diffusions in the batteryprotection structure simply make use of the source/drain implants, andthe deepest diffusion simply uses the N-Well (or P-well) fabricationsteps.

For process simplicity, the intermediate-depth diffusion is mostpreferably formed by using an implant which is identical (in dose andenergy) to another implant used in the same process. The additionaljunction depth is achieved by exposing the earlier implant to ahigh-temperature step before the later implant is performed, so that theearlier implant will have a correspondingly greater diffusion length(integral (Dt)⁰.5).

A variety of "substrate" structures are commonly used for integratedcircuits, and far more have been proposed or have seen limited use. Forexample, the "substrate" which surrounds the N-wells and P-wells isoften an epitaxial layer atop a much more heavily doped underlyinglayer. For another example, the N-wells and P-wells are commonly formedby separate implantation (and drive-in) steps, and such processes arereferred to as "twin tub" processes; but alternatively one of thesesteps may be omitted, so that, for example, the PMOS devices might beformed directly in an N-type upper substrate portion. Other importantstructure types include silicon-on-insulator structures and fulldielectric isolation structures, where there is no electricallycontinuous body linking all of the wells. It is important to note thatthe teachings set forth herein can advantageously be adapted to atremendous variety of substrate structures, including not only theembodiments listed or mentioned, but also many others.

It should be noted that the disclosed families of devices structures canalso be used for a variety of other purposes. In particular, thedisclosed structure provides a diode structure which may be adapted foruse in other types of device structures, in very-low-power integratedcircuit applications.

It should also be noted that some prior art CMOS structures have usedguard ring structures to suppress latchup. The problem of latchup(suppressing the parasitic thyristor) is a quite different problem fromthe leakage problems discussed above, but in both cases collection ofminority carriers is desirable. Guard ring structures are commonly usedto surround locations (such as output drivers) where transient signalsare most likely to cause injection of minority carriers. (A sufficientinjection of minority carriers could fire the parasitic thyristor, andthus lead to latchup.)

In the preferred class of embodiments, the diffusion structure describedis used to conserve the charge in the battery. One drain on the batteryis caused by negative excursions on an incoming data line (for example,when a negative voltage spike occurs due to an electrostatic discharge(ESD) event). In a normal battery-powered integrated circuit, thecurrent drawn during such a negative voltage surge would be drawn bothfrom the ground connection and also from the power supply connection.However, in stringently power-limited applications, even this amount ofcurrent, over the lifetime of the part, can use enough of the batterycapacity to shorten the part's lifetime substantially.

That is, when a negative transient occurs, a large number of electronswill be injected. If these electrons are allowed to diffuse freely, manyof them will diffuse toward the high-potential regions which areconnected to the battery. This charge transfer reduces the total chargeavailable during the lifetime of the battery.

The shielded diode structure of FIG. 16K is protected: almost allelectrons injected at first junction 111 will be collected at secondjunction 112. By contrast, a simple field effect transistor (FET) outputdriver, like transistor 150 in FIG. 16M, is not isolated: when the drainjunction of such an NMOS FET is forward biased, electrons will bereleased into substrate 140, and many of these electrons can thendiffuse to regions of high potential.

Therefore, a further teaching is to use the diffusion structure tosource current to negative transients which may occur on the I/O linesof a chip. In this embodiment, an I/O line is connected so that thefirst junction (in a structure as described above) will be forwardbiased when the I/O line goes negative, and the other side of the firstjunction is connected to ground potential. Thus, when a negative-goingtransient occurs, current will be sourced, through the first junction,from ground.

When a negative-going transient occurs, some current will also besourced, at the output transistor which drives the I/O line, and some ofthis current component will cause minority carrier diffusion; but theuse of this teaching helps to reduce the amount of current sourced whichcan cause minority carrier diffusion. Preferably the area of the firstjunction is substantially larger than that of the junction area of thesource/drain diffusion, in the output transistor, which is connected tothe power supply.

This teaching also has two further advantages. First, the reduced riskof minority carrier injection means that the risk of stored data statesbeing upset by transient signals is reduced. Second, the risk of latchupis reduced.

Thus, this teaching advantageously provides a battery-powered integratedcircuit which is protected against battery depletion by electrical noiseappearing at input/output connections. This teaching may be particularlyadvantageous in integrated circuits which are intended for use insystems where high levels of noise must be tolerated.

Bus Organization

To communicate with this memory, in the preferred embodiment, anone-wire bus protocol is used. This protocol is well adapted forinterface to the low-cost architecture of the module of the presentlypreferred embodiment.

Time-Domain Relations

A bidirectional one-wire bus requires some use of time-domain orfrequency-domain relations, to track the two half-channels ofcommunication.

It is quite possible to put an accurate time base in a low-powerintegrated circuit, using CMOS oscillators stabilized with quartzcrystals; but the use of such techniques adds to the cost of the part. Acrude time base can be provided simply by using an oscillator which isnot stabilized. However, the response time of a simple timing circuitwill be dependent on processing parameters. In conventional integratedcircuit processing, there will normally be significant variation inparameters such as layer thickness, line-to-space ratio, and net dopantconcentration in various locations. Thus, the electrical parameters,such as the series resistance of a polysilicon resistor of a givennominal dimension, can easily vary by +20% or more, even in awell-controlled process. This means that the net speed of a timingcircuit can vary by even more, since the net speed will be dependent onseveral electrical parameters, which may vary together or in opposition.

Parameter variation can be compensated for, by testing a newlyfabricated wafer and programming elements on-chip (such as trimmingcapacitors) to adjust the net delay of timing elements; but thisadditional manufacturing step adds significant expense.

Low-Voltage CMOS Logic

Moreover, in a low-voltage CMOS system (i.e. where the supply voltage isless than the sum of the PMOS and NMOS threshold voltages), achievingeven a crude time base is much more difficult. This is due to thetransfer characteristics of a logic gate in this technology.

FIG. 5A shows the voltage transfer characteristics (V_(OUT) graphed as afunction of V_(IN)) for an inverter in conventional CMOS technology(e.g. where the supply voltage V_(DD) is about 5 Volts, and the PMOSthreshold voltage V_(TP) and the NMOS threshold voltage V_(TN) both havemagnitudes in the range of about 0.8 V to 1.1 V.) Suppose that the inputvoltage V_(IN) was initially at ground voltage V_(SS) (0 V), so that theinverter's NMOS transistor is off and the inverter's PMOS transistor ison. Now, as V_(IN) starts to rise, V_(OUT) will stay at V_(DD) untilV_(IN) rises to V_(TN). At this point the NMOS device will start to passcurrent. However, the NMOS device will not be able to overpower the PMOSdevice until the voltage reaches a trip point V_(TRIP). The trip pointvoltage V_(TRIP) is well-defined for each particular logic gate, but isdependent on the device dimensions. (If the width of the PMOS device isincreased, or the length of the PMOS device decreased, or the width ofthe NMOS device is decreased, or the length of the NMOS deviceincreased, then the NMOS device will have more difficulty inoverpowering the PMOS device, and the trip point V_(TRIP) will occur ata higher voltage.) As the input voltage V_(IN) increases, the NMOSdevice will pass more current and the PMOS device will pass lesscurrent, until at voltage V_(DD) -V_(TP) the PMOS transistor turns off.

By contrast, the transfer characteristic of a low-voltage CMOS inverter,as shown in FIG. 5B, are quite different. (Suppose, for example, thatV_(DD) =1.5 V, and V_(TP) =V_(TN) =0.9 V. Thus, note that FIGS. 5A and5B are not drawn to the same scale.) Here there is no region where boththe NMOS and PMOS devices are on. When the input voltage V_(IN)increases above V_(DD) -V_(TP) (0.6 V in this example), the PMOS devicewill turn off, but the NMOS device has not yet turned on. Therefore,until the input voltage increases to V_(TN) (0.9 V in this example), theoutput node will be floated. (The node capacitance usually faces afairly high-impedance load, and therefore, within the time normallyrequired for the input voltage to swing across this voltage range, theoutput voltage will remain fairly constant. Moreover, a weak latch willtypically be added to bridge this dead zone.) Thus, the transfercharacteristic shown includes a significant hysteresis, since, betweenV_(DD) -V_(TP) and V_(TN), the output voltage is dependent on thedirection of change of the input voltage.

Error of Crude Time Base

A response curve like that of FIG. 5B makes it more difficult to controlthe net delay of a circuit, since small changes in electrical parametersmay produce large changes in the response characteristics. Thus, in suchlow-voltage technology, the frequency of an unstabilized oscillator mayeasily vary over a very large range (for example, over a range of 4:1),even in a well-controlled process.

The system of the presently preferred embodiment makes use of such anunstabilized oscillator to provide a crude time base within the module.This crude time base, together with electrical relationships, providesthe necessary referent for communication over a one-wire bus. The use ofa one-wire bus is very advantageous to the system user.

Electrical I/O Relationships

The bus protocol is also designed to minimize the charge transfer out ofthe battery in the module. This is done by using an "open-collector"type architecture. The protocol has been specified so that the modulenever sources current to the data line, but only sinks current.

When a data module is in contact with a host system, the host systeminitially pulls up the data line. (The module also preferably contains avery high-impedance pull-down resistor at this node, but this isincluded, in the preferred embodiment, merely to avoid the risk offloating nodes.) The host system initiates each stage of a data transferoperation by driving the data line low. The module detects this fallingedge, and one of several further events can then occur.

If the module is being read (as previously determined by overhead bits),the module, after seeing the falling edge which starts the cycle, eitherwill or will not turn on its NMOS pull-down transistor, depending on thevalue of the data bit being read at that cycle. When the NMOS pull-downis turned on, the module lets its preset timing period elapse, and thenturns off the NMOS pull-down. Thus, when the system wants to read fromthe module, it applies a falling edge, waits a short time to be surethat the module has received the falling edge, and then attempts to pullup the data line, using a pull-up resistor which is not strong enough tooverpower the NMOS pull-down transistor in the module. After waiting asufficient time for the pull-up resistor to have raised the line to ahigh level (if the NMOS pull-down is off), the system tests the datavoltage to ascertain the data bit. The system then waits for the maximumtime period of the module delay to elapse, plus enough time for the dataline to stabilize at a high level, and then sends another falling edgeto read the next bit.

If the module is being written to (as previously determined by theoverhead bits), the module, after seeing the falling edge which startsthe cycle, waits for its preset timing period to elapse, and then storesthe logic value of the data line. Thus, when the system wants to writeto the module, it applies a falling edge, waits a short time to be surethat the module has received the falling edge, and then drives the dataline either high or low, depending on the data bit. The system thenwaits for the maximum time period of the module delay to elapse,restores the data line to a high level, allows enough additional timefor the data line to stabilize at a high level (and for the edgedetector in the module to reset itself), and then sends another fallingedge to write the next bit.

Block Transfer--Overhead and Reset

All data transfers are preferably done by reading or writing the entirecontents of memory as a single serial stream. A short block of overheadbits, at the start of each transfer, defines the transfer type.

A further point of the protocol is a way to reset the module. Suppose,for example, that a module is pulled out of the slot in the middle of adata transfer, so that the memory pointer inside the module shows thatthe next bit to be written is bit number 117. The next system into whichthis module is inserted must not assume that the module's startingaddress is necessarily zero.

To make sure that the starting memory address of a newly inserted moduleis zero, as expected, the system sends a long string of write-zerocommands, followed by a write-one command. The module contains simplesequential logic, which monitors the incoming bit stream for nonstopsequences of write-zero commands. If the module receives a nonstopsequence containing as many write-zero commands as the total length ofthe memory, the counter will freeze until the chip is reset. The chipwill be reset if and only if an incoming "1" bit is seen while thecounter is frozen.

This provides a reset capability, whereby the system can ensure that thestarting address of the module is accurately known. Thus, on everyinsertion of a new module, the system can send such a reset sequence toinitialize the address pointer in the module. Note that thisaddress-pointer-reset is only necessary once per insertion. The sequenceof write-zero commands will not normally destroy data, because themodule never receives the overhead bit sequence which would tell it toenter write mode. (The only conditions under which data could bedestroyed by these commands is when the module has been interrupted inthe middle of a previous write sequence, and in this case the data maybe presumed corrupt anyway.)

Of course, the data structures inside memory would normally includeprovisions for software error protection, such as overhead bits andchecksum bits. However, a wide variety of such formatting schemes can beused, at the discretion of the user.

System Architecture

These ideas are used as parts of a very system architecture. Theelectronic module enabled by the teachings herein is extremely compactand extremely cheap. From a systems point of view, this module is insome ways more analogous to a read/write bar code than to a conventionalelectronic memory system.

Macro-System Architecture

Thus, this module can be used for price tags, for inventory tags, forwork-in-process monitoring, for retail sales (to permit customers toselect merchandise (e.g. by taking one module or a handful of modules toa cashier or to an automated checkout machine), without exposing theactual inventory to pilferage), and for a wide variety of other suchcompact data-transfer applications. Thus, the module described can beregarded as an electronic token, which is as portable and rugged as ametal token, but which is far more versatile.

This provides an large-scale systems architecture, wherein multiple hostsystems can each interface to small electronic "tokens." The tokens aresmall coin-shaped two-terminal read/write data modules, and are compact,rugged, and extremely cheap. Each of the tokens contains only twoexternal contacts, a battery, and a small amount of memory. The memoryis serially accessible, using a one-wire-bus protocol which minimizesthe drain on the battery.

Electrical Interface from Token to Standard RS232 Interface

The presently preferred embodiment also uses an electrical interface tothe tokens, which permits interfacing to tokens with a wide variety ofcomputers, including a tremendous variety of personal or othercomputers, as long as the computer includes an interface to RS232 (orsome comparable standard). The token has a one-wire-bus interface,implemented in a battery-backed open-collector architecture, whichprovides a read/write interface. The communication protocol expected bythe token has been specified so that the token never sources current tothe data line, but only sinks current. The communication protocol alsoincludes time-domain relations which are referenced to a very crude timebase in the token, and the system must preserve timing relations whichwill be satisfied by tokens in which the time base takes on any of thewide range of foreseeable speeds. To interface to this protocol, theprogrammable capabilities of the standard UART chip in the computer'sRS232 interface are exploited to provide adaptation to the time baserequirements of the module. This is done by writing an entire byte ofoutput from the UART, at a much higher baud rate than the module can berelied on to accept, to write a single bit of data into the module. Theread-data line (RX) of the UART is tied back to the transmit-data line(TX) through a resistor, so that the UART will also always report a readof the same data byte being written, unless the token has turned on itspull-down transistor. An electrical network is used at the interfacewhich (in effect) reverses the ground plane identification of the twoleads, but which does provide the correct signal polarity to the tokenfor signal discrimination in read mode.

Physical Interface for Receiving Electronic Tokens

Preferably each host system uses a physical configuration of electricalcontacts which provides rapid contact for electronic data modules(tokens). A slot, dimensioned to receive electronic tokens, includes agrounded contact positioned to make contact to the edge of a token whichmay be inserted, and two data contacts which are positioned to makecontact to the opposite faces of the token. Each of the data contacts isconnected to an open-collector driver circuit, including a pull-upresistor which will bring the potential of the contact high when theslot is empty. The token is shaped so that its edge, and one of itsfaces, are connected to the token's ground line, and the other face isthe token's data line. Thus, when a token is inserted (no matter whichway the token is facing), one of the two data contacts will beimmediately pulled to ground, by short-circuiting across the groundplane of the token. The system can thereby recognize that a token hasbeen inserted, and that the other data contact (the one which was notshorted to ground) can communicate with this token's data line. Thus,even though the token itself is asymmetric, and even though thedirectional orientation of the token is not initially known to thesystem, no physical asymmetry needs to be introduced into the token orthe slot to assure proper data interface.

Alternative Physical Interface--Hand-Held Wand

A wand which provides rapid contact to a two-terminal electronic tokendata module. The wand includes one contact which will make contact tothe periphery of an electronic token which the wand is pressed against,and one contact which will make contact to the center of the token.Preferably the wand includes a base portion which is shaped to be wornon the second joint of a user's finger. This wand can be used for veryrapid manual contacting of electronic tokens in various physicalpositions. This can be very advantageous in a variety of datacollection/updating applications such as retail checkout, or trackingwork-in-progress in a computer-assisted-manufacturing environment.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to theaccompanying drawings, which show preferred embodiments of theinvention.

FIGS. 1A and 1B show two versions of the packaged module of thepresently preferred embodiment: FIG. 1A shows a version using a packagedintegrated circuit on a flexible circuit board, and FIG. 1B shows aversion using a chip-on-board mounting with a rigid circuit board.

FIG. 2A is a timing diagram of a write-1 operation, FIG. 2B is a timingdiagram of a write-0 operation.

FIG. 3 is a timing diagram of a read operation, in the module of thepresently preferred embodiment.

FIG. 4 shows the format of the overhead bits used for each block datatransfer operation, in the module of the presently preferred embodiment.

FIG. 5A shows the voltage transfer characteristics (V_(OUT) graphed as afunction of V_(IN)) for a typical inverter in conventional CMOStechnology (where V_(DD) >V_(TP) +V_(TN)).

FIG. 5B shows the transfer characteristic for a typical inverter in alow-voltage CMOS technology (where V_(DD) <V_(TP) +V_(TN)).

FIG. 6 is an overview of the physical organization of the integratedcircuit which is used, in the presently preferred embodiment, in themodule of FIG. 1.

FIG. 7 shows the electrical organization of the integrated circuit ofFIG. 6.

FIGS. 8A and 8B are two parts of a single Figure which shows theone-wire-to-three-wire conversion circuit used, in the presentlypreferred embodiment, in the integrated circuit of FIG. 6.

FIGS. 9A and 9B are two parts of a single Figure which shows the controllogic used, in the presently preferred embodiment, in the integratedcircuit of FIG. 6.

FIG. 10 shows the electrical organization of the memory, in thepresently preferred embodiment, in the integrated circuit of FIG. 6.

FIG. 11 shows a memory cell, which can operate as a RAM cell, or whichcan be programmed to operate as a ROM cell.

FIG. 12 shows a sample host system, which can interface to electronictoken modules like the module of FIG. 1.

FIG. 13 shows the single-ended sense amplification stage used in thememory of FIG. 10, in the presently preferred embodiment.

FIG. 14 shows the bitline precharge and pull-up logic used in the memoryof FIG. 10, in the presently preferred embodiment.

FIGS. 15A, 15B, and 15C show the finger-mounted wand used, in thepresently preferred system embodiment, for manually contacting multipleelectronic tokens successively.

FIGS. 16A-1 through 16A-8 relate to several embodiments of a batteryprotection diode, of which one version is preferably used in theintegrated circuit of FIG. 6. It should be appreciated that thesedrawings are not necessarily drawn to scale, and, in particular, thatsome of the vertical dimensions in the device sections shown have beenexaggerated for clarity.

FIG. 16B illustrates a cross-sectional diagram of a prior art batteryprotection circuit.

FIG. 16C illustrates a schematic diagram of the parasitic PNP transistorin the prior art structure of FIG. 16B.

FIG. 16D illustrates a cross-sectional diagram of a first sampleembodiment of the disclosed battery protection circuit.

FIG. 16E illustrates an electrical schematic of the parasitic PNPtransistors of the battery protection circuit of FIG. 16D.

FIG. 16F illustrates a top view of the battery protection circuit ofFIG. 16D.

FIG. 16G illustrates a cross-section of a portion of the structure shownin FIG. 16D.

FIG. 16H illustrates a dopant profile of a sample embodiment of thebattery protection circuit of FIG. 16D.

FIG. 16I illustrates a cross-sectional view of an alternate embodimentof the disclosed battery protection circuit utilizing aSilicon-On-Insulator construction.

FIG. 16J illustrates a cross-sectional diagram of yet another embodimentof the disclosed battery protection circuit, wherein the structure isfabricated in an epitaxial layer disposed on top of semiconductormaterial.

FIG. 16K shows an example of a battery protection circuit in a CMOSintegrated circuit with a P-type substrate.

FIG. 16L shows a test structure which is similar to the device structureof FIG. 16K.

FIG. 16M shows test data for this structure.

FIG. 16N shows a further alternative embodiment, wherein a diffusionstructure is connected to provide ESD protection for an I/O connectionof a battery-powered integrated circuit.

FIG. 16P shows test data for the device structure of FIG. 16N.

FIG. 17 shows the configuration of contacts used, in one embodiment, ina host system to contact electronic tokens.

FIG. 18 shows the electrical driver configuration used on the host side,in one class of embodiments, to interface to electronic tokens.

FIG. 19 shows a network used, in another embodiment, to interface from aserial port to an electronic token.

FIG. 20 shows timing relations preferably used, in a sample embodiment,for interfacing from a standard RS232 port to an electronic token.

FIG. 21 is a block level schematic of a further preferred embodiment.

FIGS. 22A-N are schematic circuit, timing, and state diagrams of theembodiment of FIG. 21.

FIGS. 23A-S are schematic memory organization, command flowchart, andcommand structure diagrams.

FIGS. 24A-E show various connections of the embodiments on printedcircuit boards.

FIG. 25 schematically illustrates an EPROM embodiment.

FIGS. 26A-D show parallel port connections of the embodiments.

FIG. 27 illustrates the hardware arrangement for a module access system.

FIGS. 28A-B show blocks and circuitry for embodiments including a clockor counter.

FIGS. 29A-F illustrate embodiments with an additional terminal.

FIGS. 30A-C show a packaging scheme for an embodiment of FIGS. 29.

FIGS. 31A-B illustrate an embodiment application in a mouse.

FIG. 32 shows an embodiment application for adjustment control.

FIG. 33 is a schematic diagram of a module battery test circuit.

FIGS. 34A-C show modules and host communication by radio waves.

FIGS. 35A-C illustrate alternative token packaging of embodiments and atoken reader.

FIG. 36 is a schematic circuit diagram of a bus repeater.

FIGS. 37A-B illustrate a 1-wire to 3-wire interface arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The numerous teachings of the present application will be described withparticular reference to the presently preferred embodiment. However, itshould be understood that this class of embodiments provides only a fewexamples of the many advantageous uses of the teachings herein. Ingeneral, statements made in the specification of the present applicationdo not necessarily delimit any of the various claimed inventions.Moreover, some statements may apply to some inventive features but notto others.

Physical Packaging of Module

FIGS. 1A and 1B show the relation of assembled elements, in two versionsof the packaged module of the presently preferred embodiment. (FIG. 1Ashows a version using a packaged integrated circuit on a flexiblecircuit board, and FIG. 1B shows a version using a chip-on-boardmounting with a rigid circuit board.) Note that the module shownincludes an integrated circuit and a battery. The module is preferablycoin-shaped, and the two faces of the module are isolated from eachother.

To fit the integrated circuit into this very small space, a packagingscheme is used in the preferred embodiment. A two-part metal containeris used, which has two shallow concave pieces 0100A and 0100B which fittogether to form cavity 101. The integrated circuit (in a low-heightpackage 0130, such as a flat-pack or SOIC) is mounted on a very smallflexible printed circuit board 0120, which fits inside the container0100. Laterally spaced from the integrated circuit 0130, on the otherend of the small flexible board 0120, the board end is sandwichedbetween a battery 0110 and a piece of elastic conductive material 0140(such as conductive plastic foam). Thus, the battery 0110 is connectedbetween one face 0100B of the container 0100 and a power conductor (notshown) on the board 0120. The piece of elastic conductive material 0140makes contact between a data trace (not shown) on the board 0120 and theother face 0100A of the container 0100. Another trace (not shown) on theboard 0120 makes contact directly to the container face 0100B on whichthe battery's ground terminal is connected. Thus, simple wiring on thesmall board 0120, using through-hole vias, suffices to route power,ground, and data lines to the integrated circuit 0130, while providing asealed durable package with two external contacts.

In the alternative embodiment of FIG. 1B, a small rigid circuit board0120' is used in place of the flexible board 0120. Note that anadditional piece of conductive foam 0142 is used in this case, toprovide electrical contact from a trace on the board 0120' to the groundside 0100B of the casing. Note also that, optionally, an insulatingadditional piece of foam 0142 provides spacing between the board 0120'and the casing piece 0100A. Note also that a chip-on board mounting0130' is used instead of the package 0130.

The casing halves 0100A/100B are preferably parts of a standardelectronic battery package. Such a casing can be hermetically closed,simply by swaging the two parts together with sealant at their join. Inthe presently preferred embodiment, the casing 0100 has externalfinished dimensions (after the case is sealed) of 16 mm wide and 3.2 mmthick, and the battery 0110 is battery type AG1. However, of course, awide variety of other dimensions and battery types can be used, as longas the dimensions are compatible.

The battery is preferably a low-voltage battery (1.5 V, in the preferredembodiment.) This is cheaper, and maximizes power efficiency, butrequires some circuit design features to accommodate the electricalinterface. (Electronic watches have often been powered by 1.5 Vbatteries, but such devices do not have any direct electrical interfaceto the outside world. By contrast, the module of the presently preferredembodiment communicates over a one-wire bus which is driven by full CMOSvoltage levels.)

The integrated circuit, in the preferred embodiment, contains 256 bitsof serial-access memory. This memory is read- or write-accessed as asingle block transfer. It is contemplated that larger amounts of memorymay be advantageous. Of course, other types of memory organization canbe used instead; but for many applications it is contemplated that useof a very small amount of memory (4K or less) may be particularlyadvantageous, since this extends the battery lifetime.

Module Mounting and Adhesion

In many applications (such as inventory control, machinery maintenancerecords, or retail tagging) users will prefer to affix the tokens to thephysical items to which the data in the individual tokens refers. Inthis case, the token must be mounted so that both terminals of the tokencan be contacted by the user. In the presently preferred embodiment(using a package like that shown in FIG. 1A), only one of the possibleorientations will work. (The inner casing piece 0100A must be exposed,and therefore, if the token is to be mounted on a surface, it is theouter casing piece 0100B which should be adhered to the surface.)

For such applications, the packaged modules (in embodiments usingpackages like those of FIGS. 1A and 1B) are preferably shipped withdouble-sided adhesive tape already affixed to the side of the modulewhich is to be adhered to a surface (face 0100B, in the example of FIG.1B).

Preferably the double-sided tape has a high-tack face adhered to thecasing piece 0100B. The other side of the tape may be high-tack, forpermanent mounting; or may be low-tack, for applications (such asretail) where the tokens will be frequently reused; or may bemedium-tack. For many applications, the tokens can be advantageouslyshipped with the low-tack face of many tokens stuck to a common coversheet.

Integrated Circuit Organization

FIG. 6 is an overview of the physical organization of the integratedcircuit which is used, in the presently preferred embodiment, in themodule of FIG. 1. This is a fairly small integrated circuit, with a diesize, in the preferred embodiment, of about 2,000 mil² (in 1.2 microntechnology).

The incoming ground line is connected to a contact pad 612, and theincoming data line is connected to a contact pad 611, in an area 610which contains I/O and ESD circuitry. (The battery terminal is connectedto a third contact pad 613.) The contact pad 611 is connected to a largepull-down transistor 614, and to an ESD protection structure 618/619,which will be described in detail below. A very weak transistor 615,which is connected to be always turned on, is connected in parallel withthe driver transistor 614, to provide a high-impedance leakage pathwhich brings the two terminals of the module toward the same potentialwhen the module is not connected to a system.

The incoming data interface is provided by 1-wire-to-3-wire conversioncircuitry 630, which implements the one-wire bus protocol. Thisconversion circuitry connects to the memory 640, and to the controllogic 620, through a more conventional three-wire bus (including data,clock, and reset lines).

The memory 640 is internally configured as a random-access memory array(although the host can only access the memory serially, as a singleblock). The memory includes peripheral logic 642, and two arrayportions. The overall array dimensions, in the preferred embodiment, are16 rows by 16 columns, but two rows (shown as area 644) are preferablyformed of RAM/ROM hybrid cells, which will be described below. The cellsin the other 14 rows (shown as area 646) are conventional six-transistorSRAM cells.

Of course, a wide variety of other array sizes and layouts can also beused, as will be obvious to those skilled in the art of memory design.In fact, it is contemplated that, in the near future, the memory arraysize may be advantageously increased from 256 bits to 1024 bits.

FIG. 7 shows the electrical organization of the integrated circuit ofFIG. 6. The RAM 640 receives ten address bits Q0-Q9 from the controllogic 620, as well as control signals ER2, SDOUTB, and RESET. Controlsignal ER2 enables the RAM. Control signal EWD selects read or writemode. Control signal SDOUTB is a strobe signal, which latches a datastate for output. The RAM 640 also receives a data input DATIN, and canprovide a data output DATOUT.

The 1-wire-to-3-wire conversion circuitry 630, in the preferredembodiment, interfaces from the external data line to a moreconventional 3-wire serial bus, which includes RESET, CLOCK, and twodata lines (DATIN and DATOUT). The control logic 620 also provides anoutput "210", which indicates when the counter is frozen. (This signalis used in implementing the reset logic, as discussed below.) The1-wire-to-3-wire conversion circuitry 630 provides a timing output QXF1,which corresponds to the output pulse of a one-shot. (This pulse may befrom 15 to 60 microseconds wide, and provides the basic timing referenceinside the token module.)

FIGS. 8A and 8B are two parts of a single Figure which shows the1-wire-to-3-wire conversion circuitry 630 which is used, in thepresently preferred embodiment, in the integrated circuit of FIG. 6.Every falling edge in the incoming data line I/O PAD fires a one-shot toproduce a pulse on the line QXF1. (This pulse, in the presentlypreferred embodiment, has a width of 15-60 microseconds, and providesthe time reference within the module.) In turn, every falling edge ofsignal QXF1 generates a short pulse (about 1.5 microseconds wide) on theCLOCK line. RESET signals are generated by simple logic which implementsthe conditions for reset, as described below.

FIGS. 9A and 9B are two parts of a single Figure which shows the controllogic used, in the presently preferred embodiment, in the integratedcircuit of FIG. 6. After the protocol register 920 has been loaded,counter chain 910 counts successive clock pulses. (Every falling edge onthe data line will lead to a clock pulse within the module, and thesepulses are counted by counter 920.) The counter 910 is also connected tologic which will intercept the clock signal (to freeze the count), andactivate signal 210, as soon as 256 bits of data have been read orwritten. (Note that the counter chain shown actually includes two morestages than are needed. This permits ready modification for 1024-bitembodiments.) Register 920 receives the protocol word. The stages ofthis register are connected so that a RESET will set the first stage,and clear the other stages. Thus, when a 1 propagates through to thelast stage, a protocol word has been loaded.

FIG. 4 shows the format of the protocol word, in the module of thepresently preferred embodiment. Note that the first bit of the protocolword is always a 1. Note also that two bits have been reserved formodule identification. Thus, memory expansion can be easily achieved bywiring as many as four memory chips in parallel, in a single tokenmodule. Note also that the read/write selection bits provide significantprotection against accidental writes, in a high-noise environment.

Low-Voltage SRAM Architecture

Among the teachings set forth in the present application is a low-powerlow-voltage CMOS six-transistor static random access memory (SRAM),which can operate on a power supply voltage which is less than the sumof the NMOS and PMOS threshold voltages, and which does not include anyanalog or metastable sense amplifier stages. The selected cell isallowed to pull one of its bitline pair all the way down to ground.Thus, full logic levels appear on the bitline pair. Only one line of thebitline pair is connected to the following gate stage. Preferablybitline precharge transistors are connected to pull up all bitline pairswhenever the RAM is not selected.

Process Characteristics

In applications such as those of the preferred system embodiment, it ishighly desirable to minimize unnecessary charge consumption. Inparticular, this means that the area-specific junction leakage of thesemiconductor material, for the source/drain junctions, at 5 Volts andat 25 C, should be low (preferably much less than 1 femtoAmperes persquare micron). For example, the process used in the presently preferredembodiment has junction leakage, for the source/drain junctions, in theneighborhood of about 100-200 attoAmperes per square micron at 25 C andat 5 Volts. (As is well known, this parameter has a strong temperaturedependence. For example, the process used in the presently preferredembodiment has junction leakage, for the source/drain junctions, in theneighborhood of a few femtoAmperes per square micron at 25 C and at 5Volts.) Such low leakage is achieved, as is well known to those in thesemiconductor art, by using good quality monocrystalline siliconstarting material with low levels of carbon and transition metals;optionally, growing epitaxial silicon on the starting wafers; rigorouslyisolating wafers in process from heavy metal contamination; minimizingthe exposure of wafers in process to ionizing radiation, from sourcessuch as implanters; and other such well-known precautions.

Electrical Organization

FIG. 10 shows the electrical organization of the RAM 640, in thepresently preferred embodiment, in the integrated circuit of FIG. 6.Five address bits are connected to row predecoder/decoder 1010, and fivebits are connected to column predecoder/decoder 1020. (As noted above,it is contemplated that expansion to an array of 1024 bits may beadvantageous, and the extra address bits are provided for thiscontingency.) The eight primary address bits provide 16 select lines, tothe 16 parallel blocks of column driver logic 1030, to select a column.The column driver logic contains precharge transistors, and alsocontains pass gates which connect the selected column to a write drivercircuit 1032 (in write mode) or to sense amplifier 1034 (in read mode).

Precharge Operation

The column lines (bitline pairs) are always held high when the memory isdeselected. When the memory is selected, the bitline pairs are floated(until a row of cells turns on, and begins to pull down one side of eachbitline pair). This always-high operation helps to provide powerefficiency: one-half of the bitlines are discharged for each one-bitdata access, but not under any other circumstance. Thus, the net chargeconsumption per access is acceptably low.

Sense Amplification and Output

The "sense amplifier" circuit 1034 does not function at all similarly toa conventional memory sense amplifier: this amplifier is a simpledigital circuit, which receives a single-ended output, from only one ofthe bitlines in a bitline pair. (However, the write driver isdouble-ended, since one of the bitlines must be driven low.)

FIG. 14 shows the bitline precharge and pull-up logic used for eachcolumn of the memory of FIG. 10, in the presently preferred embodiment.Note that full CMOS transmission gates are used to pass the output ofthe selected column. (This is required by the low operating voltagepermitted in the presently preferred embodiment.) PMOS transistors 1420,when gated by signal EC, precharge the bitline pair C and CB to V_(DD).When a selected cell begins to pull down one side of the bitline pair(either line C or line CB), one of the cross-coupled PMOS transistors1430 will turn on (after the line sinks below V_(DD) -V_(TP)) to holdthe other side of the bitline high. (Since the bitline was alreadyprecharged high, this transistor is not expected to source large amountsof current. These transistors are provided primarily to avoid the riskof a floating node.)

FIG. 13 shows the single-ended sense amplification stage used in thememory of FIG. 10, in the presently preferred embodiment. The inputlabelled D is one side of a column bitline pair C and CB, selected byone of the selection gates shown in FIG. 14. Note that the first stageinverter 1310 is preferably asymmetric. In the presently preferredembodiment, this inverter includes a PMOS device which is 30 micronswide and 1.2 microns long, and an NMOS device which is 3 microns wideand 3 microns. This asymmetry helps to assure that inverter 1310 willswitch strongly as soon as it receives a signal from a bitline which isbeing pulled down by the driver transistor in a cell. (In a normal CMOScircuit, this asymmetry would shift the trip point of the logic stage.However, in this low-voltage logic, this is not true, due to thehysteresis effect discussed above with reference to FIGS. 5A and 5B.)The output of inverter 1310 is loaded by capacitor 1320. This capacitiveloading helps to provide data hold time after signal SDOUTB ends. Thefollowing inverters, in the preferred embodiment, have more normalrelative device sizings (nominal W/L: PMOS 10/1.2, NMOS 5/1.2). Theresulting logical signal is fed into a gated latch 1330, which isclocked by signal SDOUTB. Note that the latch is clocked in two places,so that the feedback connection is broken (by full CMOS transmissiongate 1332) whenever full CMOS transmission gate 1334 tums on to admit anew data value. This prevents contention and saves power.

RAM/ROM Hybrid Memory

Another teaching set forth in the present application is a memory cellwhich can operate as a static RAM, or can be programmed to operate as aROM cell. Thus users who need the extra security permitted by ROMencoding can have this capability, while users who do not need ROMencoding can use off-the-shelf parts as RAM only.

FIG. 11 shows a memory cell, which can operate as a RAM cell, or whichcan be programmed to operate as a ROM cell. The signal RE is itselfderived from a fuse, and, if ROM operation has not been enabled, thissignal will be low. Thus, in RAM mode, the cross-coupled inverters 1110will provide normal latch operation, selectively accessed by passtransistors 1120.

When it is desired to convert a block of memory to ROM, a fuse is blownto hold the RE signal high. In addition, one of the two fuses 1130 isblown in each cell, to encode either a "1" or a "0". Thereafter, one ofthe two nodes of the latch will always be pulled to ground. Even if thecell is addressed in a write operation, the connection to ground willeasily overpower the PMOS load transistor, to hold the latch in itspermanently programmed state. (In the presently preferred embodiment,the NMOS driver transistors in the inverters 1110 each have nominal W/Ldimensions of 8/1.2 microns, the PMOS load transistors in the inverters1110 each have nominal W/L dimensions of 6/6 microns, and the NMOSROM-mode transistors 1140 and the NMOS pass transistors 1120 each havenominal W/L dimensions of 4/1.2 microns.)

ESD Protection

The systems environment described above means that the data modules facesome unusual integrity requirements. Since the modules may be exposed tovery rough treatment, in consumer and industrial environments, theyshould preferably have a very high level of immunity to electrostaticdischarge (ESD).

ESD Protection Diode Profile

Referring now to FIG. 16B, there is illustrated a cross-sectionaldiagram of a semiconductor substrate 10 utilizing a prior art batteryprotection device. In this type of device, a battery terminal 12 isprovided for being connected to a battery (not shown) and an externalvoltage terminal 14 is provided for being connected to an external(system) supply voltage V_(EXT). The battery terminal 12 is typically ata lower voltage than the external supply voltage V_(EXT). For example,the battery voltage for most battery-backed systems is typically aroundthree volts, whereas the external voltage V_(EXT) is typically aroundfive volts.

The external supply terminal 14 is connected to the substrate 10, whichis an N-type semiconductor substrate in this example, through an n+contact region 16. The battery terminal 12 is connected to a P-well 18through a p+ contact region 20. The boundary of the P-well 18 forms a PNjunction 22. Therefore, when the N-type substrate 10 is at a lowerpotential than the battery terminal 12, current will flow through theforward biased PN junction 22 from the battery terminal 12. However,when the external supply terminal 14 is a higher voltage than thebattery terminal 12, the PN junction 22 is reverse biased and blockscurrent. This essentially prevents current flowing from the externalterminal 14 to the battery terminal 12 and thus charging the battery.

In a typical CMOS semiconductor device utilizing P-wells and N-wells ina twin-tub process, there will be additional P-wells that are separatedfrom the P-well 18. One of these is represented by a P-well 24, which isdisposed in the N-type substrate 10 and separated from the P-well 18 bya predetermined minimum spacing in the N-type substrate 10. A PNjunction 25 is formed between the N-type substrate 10 and the P-well 24.The P-well 24 can be utilized to configure any type of device. In orderto contact the P-well 24, a p+ contact 26 is provided which is connectedto an external circuit terminal 28. It should be understood that theillustrated structure merely represents a partial example of such aP-well structure. (For example, such a P-well would usually include atleast two shallow N+ diffusions, to provide the source/drain regions ofan MOS transistor. Such a P-well may contain three or more such N+diffusions, to provide more than one transistor, and may also beconfigured to provide other elements as well, e.g. diodes orcapacitors.)

A problem arises with the prior art device whenever the external voltagefalls (e.g. when the terminal 14 is disconnected from V_(EXT), or thesystem power supply fails), so that the external circuit terminal 28 isconnected to a voltage lower than the battery terminal. In the structureshown in FIG. 16B, this will reverse bias the PN junction 25. In thismode, minority carriers (holes, in this example) which are injected intothe substrate 10 at the forward biased PN junction 22 can be collectedat the PN junction 25. This results in the formation of a leakyparasitic PNP transistor. This parasitic PNP transistor is illustratedin FIG. 16C. This transport of holes creates a net current, from thebattery terminal 12 to the ground terminal 28, which dissipates power.

The parasitic transistor of FIG. 16C has the emitter junction formedbetween the P-well 18 and the N-type substrate 10 with the batteryterminal 12 providing the emitter terminal. The base is formed by theN-type substrate 10 with the base terminal comprising the externalvoltage terminal 14. The collector junction is formed between the P-well24 and the N-type substrate 10 with the external circuit terminal 28representing the collector terminal. It can be seen that whenever theexternal voltage terminal 14 is disconnected, the parasitic transistorillustrated in FIG. 16C passes leakage current. This results in leakagecurrent, which, in a relatively low power device, can comprise asignificant portion of the supply current, since there are usually anumber of adjacent P-wells on the substrate with a parasitic transistorconnected to each of the adjacent P-wells. Since the bases of all ofthese transistors will be common, this effectively forms amulti-collector parasitic transistor.

FIGS. 2 and 8 show two important embodiments of the disclosed diodestructure. In each, the battery power input is connected through a firstjunction 111, so that the battery cannot be charged when the external(system) power supply is active. The battery isolation diode junction111 is surrounded by a second junction 112. In the embodiment of FIG.16D, the first junction 111 is the boundary of P+ first region 36 andN-type second region 34, and the second junction 112 is the boundary ofN-type second region 34 with P-type third region (P-well) 32. In theembodiment of FIG. 16K, the first junction 111 is the boundary of P-typefirst region 121 and N-type second region 122, and the second junction112 is the boundary of P-type first region portion 121B with P-typethird region 113. Note that, in FIG. 16D, the second region 34 enclosesthe first region 36, whereas, in the embodiment of FIG. 16I, the firstregion 121 encloses the second region 122.

The second junction 112 is preferably shorted out, by a wired connectionwhich makes ohmic contact to the semiconductor regions on both sides ofthe junction. In the embodiment of FIG. 16D, the wiring 43 which shortsout the second junction makes ohmic contact to the second region 34 atN+ diffusion 40, and makes ohmic contact to the third region 32 at P+diffusion 38, and is also ohmically connected to N-type extended region(substrate) 30 at N+ diffusion 42, and is also tied to external supplyvoltage V_(EXT). In the embodiment of FIG. 16K, the wiring 131 whichshorts out the second junction makes ohmic contact to the first region121 at P+ diffusion 121A, and makes ohmic contact to the third region113 at N+ diffusion 113A, and is also ohmically connected to the batteryterminal V_(BAT).

The built-in potential of second junction 112 provides efficientcollection of minority carriers, which will recombine in theneighborhood of this junction. Thus, the second junction collects theminority carriers which can be generated when the first junction 111 isforward biased (i.e. when the integrated circuit is being powered fromthe battery). Otherwise, minority carriers could diffuse to otherjunctions, to cause leakage currents which can significantly degrade thelifetime of a low-powered device.

Note also that the structures of FIG. 16D and FIG. 16K both include anintermediate-depth diffusion, with a junction depth which issignificantly deeper than the source/drain junction depth, butsignificantly shallower than the depth of the well. In the embodiment ofFIG. 16D, this intermediate-depth diffusion is provided by the N-typesecond region 34. In the embodiment of FIG. 16K, this intermediate-depthdiffusion is provided by the P-type first region portion 121A.

Referring now to FIG. 16D, there is illustrated a cross-sectionaldiagram of a preferred embodiment of the disclosed battery protectioncircuit, as implemented in an N-type substrate 30. A P-well 32 is formedin the N-type substrate 30, having a depth of approximately fourmicrons. An N-type region 34 is formed in the P-well 32 to a depth ofapproximately 0.8 microns. A p+ region 36 is formed within the N-typeregion 34. In this sample embodiment, the p+ region 36 has a thicknessof approximately 0.40 microns. A p+ contact 38 is provided thatsurrounds or forms a ring around the N-type region 34 to provide acontact to the P-well 32. In a similar manner, an n+ contact 40 isprovided that surrounds the p+ region 36 to provide contact from thesurface to the N-type region 34. An n+ contact 42 is provided in theN-type substrate 30 outside the boundaries of the P-well 32. Theexternal voltage terminal 14, having the voltage V_(EXT) connectedthereto, is interfaced with the n+ region 42. In a similar manner, thebattery terminal 12 is interfaced with the p+ region 36. In addition,the external voltage terminal 14 is connected to the p+ region 38 and tothe n+ region 40 through an interconnect line 43.

The P-well 24 and associated p+ region 26 and external circuit terminal28 are also provided in the substrate 30 to illustrate the formation ofthe reverse biased PN junction 25. As will be described hereinbelow, thedisclosed battery protection circuit prevents conduction from thebattery terminal 12 to the PN junction 25 when the PN junction 25 isreverse biased. For illustrative purposes, the external circuit terminal28 is connected to a voltage lower than the battery terminal, forexample, zero volts.

The parasitic transistors formed in the structure of FIG. 16D areillustrated in FIG. 16E. A first PNP transistor 44 is formed having theemitter thereof connected to the battery terminal 12, the base thereofconnected to the collector thereof and the collector thereof connectedto the emitter of a second PNP transistor 46. The second PNP transistor46 has the base thereof connected to the external supply terminal 14 andalso connected to the emitter thereof. The collector of the second PNPtransistor 46 is connected to the external circuit terminal 28. Thetransistor 44 has the emitter thereof formed by the junction between thep+ region 36 and the N-type region 34, the base thereof formed by theN-type region 34 and the collector thereof formed by the junctionbetween the N-type region 34 and the P-well 32. The transistor 46 hasthe emitter thereof formed by the junction between the P-well 32 and theN-type region 30, the base thereof formed by the N-type region 30 andthe collector thereof formed by the junction between the N-type region30 and the P-well 24.

In operation, the P-type transistor 44 has the base thereof connected tothe collector, and thus, it is configured as a diode. This allowscurrent to flow through the collector of transistor 44 when the batteryterminal 12 is at a higher voltage than the N-type substrate 30.However, the emitter-to-base junction of transistor 46 is shorted,thereby inhibiting operation of the transistor 46. Therefore, when theexternal voltage terminal 14 is at a lower voltage than the batteryterminal 12, there is no parasitic transistor operation that results inleakage from the battery terminal 12 to the P-well 24.

Referring further to FIGS. 2 and 3, conduction in the parasitictransistor of the prior art normally occurs as a result of minoritycarriers being injected into the N-type substrate 30 and being collectedin the P-well 24. This collection is a result of the reverse biased PNjunction 25. In order to prevent conduction in the parasitic transistor,it is necessary to prevent either injection of the minority carriersinto the N-type substrate 30, or prevent subsequent collection thereofby the P-well 24. This, in effect, kills the gain of the parasitictransistor.

In the disclosed battery protection circuit, the minority carriers existin the N-type region 34 as holes. The P-well 32 is biased at the samepotential as the N-region 34 and therefore acts as a collector for theminority carriers or holes. However, it should be understood that anybarrier which prevents migration of minority carriers over to the PNjunction 25 to allow collection there by the P-well 32 will produce thesame result. For example, an insulating layer could be utilized thattotally encloses the N-type region 34, which insulator would adequatelyprevent minority carrier injection. Further, the holes, which arecollected in the P-well 32, could be recombined in a very heavily dopedN-type region that was disposed around the N-region 34 in place of theP-well 32. This would effectively perform a recombination of the holestherein to prevent the holes from migrating into the N-type substrate30. This heavily doped N-type region could also be disposed around theP-well 24.

With further reference to FIG. 16D, the P-well 32 is provided as acollector of minority carriers. The purpose of the electrical connection43 is to provide a path for free electrons or majority carriers. Theholes generated in the N-type region 34 as a result of the forwardbiased PN junction between p+ region 36 and N-type region 34 arerecombined at the junction between the electrical connection 43 and then+ region 40, thus preventing the minority carriers from flowing throughelectrical connection 43 to the N-type substrate 30. It is possible thatthis electrical connection 43 could be replaced by a conductive n++ plugthat is disposed through the P-well 32 to the N-type substrate 30 toconnect the N-region 34 and the N-type substrate 30. However, anelectrical connection would still be required between the P-well 32 andthe N-type region 34 to provide the correct bias therefore.

Although the just-described embodiments of the disclosed batteryprotection circuit were described with respect to an N-type substrateand parasitic PNP transistors, it should be understood that the dual ofthis structure could provide the same result wherein the battery voltagewere a negative voltage and the overall system operated on a negativevoltage. For example, the battery diode protection circuit would nowhave an n+ region connected to the battery and a P-type region providingthe other side of the diode. An N-well would be disposed therearoundisolating the diode from a P-type substrate. The N-well would providethe minority carrier isolation and act as a collector therefore, theminority carriers being electrons in this case. This would preventminority carriers from being collected in an adjacent N-well to form aleaky NPN transistor.

Referring now to FIG. 16F, there is illustrated a top-level diagram ofthe structure of FIG. 16D. The p+ region 36 is formed as an elongatedimplant that is surrounded by the n+ region 40. The n+ region 40 is inturn surrounded by the p+ region 38. The N-type region 34 to which then+ region 40 is connected, does not extend entirely under the n+ region40 to the exterior boundary thereof. Rather, the external boundary ofthe N-type region 34 is defined by a border 48. A detail of the N-typeregion 34 is illustrated in FIG. 16G. The P-well 32 is illustrated assurrounding the p+ region 38. The n+ region 42 is formed from anelongated implanted region that is disposed adjacent to the P-well 32.In a similar manner, the P-well 24 is also elongated and disposedadjacent the n+ region 42 with the p+ region 26 disposed within theP-well 24 and also having an elongated configuration.

In this embodiment, the disclosed battery protection circuit isinterleaved with a standard twin tub CMOS process flow. In the standardprocess, N- and P-channel device regions are defined and then a P-wellformed by implanting boron into the N-channel device region and anN-well formed by implanting phosphorous into the P-channel deviceregion. These implants are then driven down into the substrate and thenactive regions defined therein and separated by a layer of field oxide.Typically, a layer of nitride is disposed over a thin oxide layer todefine the active regions and then a field oxide grown on the portionsof the substrate not having nitride formed thereover.

After formation of the field oxide isolation regions, the residualnitride layers are removed. There is still a layer of gate oxide overthe active region remaining on the surface thereof. The surface is thenmasked for the implanting of the N-type region 34. This implant isachieved with phosphorous at an energy level of 180 KeV at a dosage of5×10¹³ cm⁻². After implanting of the N-type region 34, the residualoxide on the surface of the active region is removed and then a stripgate oxide is formed over the substrate. The active regions are thenimplanted to adjust the transistor threshold voltages.

After threshold voltages are adjusted, the strip gate oxide is removedand the final gate oxidation is performed, followed by polysilicondeposition and subsequent doping thereof. The poly is then patterned andetched to define the various gates and interconnects at a first level ofpoly. The N-channel source and drain areas are then defined to form thesource/drain implants. This is an n+ implant utilizing arsenic, whichimplant is also utilized to form the n+ regions 40 and 42. The substrateis then masked to form the p+ source/drain implants, at which time thep+ regions 36, 38 and 26 are formed. Thereafter, the interlevel oxide isformed by depositing oxide thereover and this oxide is subjected to athermal cycle to reflow the oxide and to provide the source/drainactivation and drive steps. The subsequent contacts are then defined andetched and then a layer of metal deposited thereover. The metal layer isthen patterned and etched to define the various metal interconnects.

Referring now to FIG. 16H, there is illustrated a vertical dopantprofile through regions 36, 34, and 32 of FIG. 16D. The dopant profileillustrates that the p+ region 36 has a surface concentration ofapproximately 1×10²⁰ cm⁻³ and a thickness of approximately 0.35 microns.The N-type region 34 has a thickness of approximately 0.4 microns with apeak concentration of approximately 4×10¹⁷ cm⁻³. The concentration levelof the P-well 32 is approximately 1×10¹⁶ cm⁻³. Therefore, the PNPtransistor 44 formed by the p+ region 36, the N-type region 34 and theP-well region 32 has a base width of approximately 0.4 microns.

Referring now to FIG. 16I, there is illustrated an alternate embodimentof the disclosed battery protection circuit. In this alternateembodiment, the diode structure of the present invention is formed in anN-type substrate 50, which N-type substrate 50 is disposed over a layerof insulating material 52. This is normally referred to asSilicon-On-Insulator (SOI) technology. In this type of technology, anN-type substrate is first formed and then a layer of insulating materialformed on the lower surface thereof. The N-type substrate 50 istypically dimensioned to equal the thickness of the P-well 32 and theP-well 24 such that no N-type material is disposed therebelow. In thismanner, isolation between laterally disposed devices is increased.

There are numerous techniques for fabricating integrated circuitsutilizing SOI technology. Some of these techniques require formation ofthe active device on the surface of an N-type substrate followed bydeposition of a thick layer of oxide and polysilicon thereover. Thesubstrate is then held from the upper side and the lower surface thereofetched down a predetermined distance. Typically, some type of heavilydoped buried layer is implanted into the substrate to form an etch stoplayer. The insulator is then formed on the remaining surface of thesubstrate under the active devices, the thick layer of polysilicon andoxide removed and the final patterning performed on the upper surface ofthe substrate. However, this is only one technique and numerous othertechniques are available for realizing SOI technology.

Referring now to FIG. 16I, there is illustrated yet another embodimentof the disclosed battery protection circuit. An N-type substrate 54 isprovided upon which a layer of epitaxially grown N-type semiconductormaterial 56 is grown. The P-well 24 and the P-well 32 are then formedtherein with the N-type epitaxial layer 56 having a thicknessapproximately equal to that of the P-wells 24 and 32. The N-typesubstrate 54 has a higher doping level than the epitaxial layer 56,resulting in the parasitic transistors being confined primarily to theepitaxial layer 56. The epitaxial layer 56 is formed utilizingconventional processes well-known in the art.

In summary, there has been provided a battery protection device thatreduces leakage due to the existence of a parasitic PNP transistorbetween the battery terminal and an adjacent P-well. The batteryprotection device includes a diode that is enclosed by a layer of P-typematerial. The layer of P-type material is operable to collect minoritycarriers to prevent collection thereof by an adjacent P-well with areverse biased PN junction.

FIG. 16K shows another embodiment of the disclosed battery protectioncircuit, which has been found to be advantageous for use with P-typesubstrates. This is the embodiment which is preferably used, with thelayout shown in FIG. 16A, in the integrated circuit layout of FIG. 6.Specifics for this embodiment will be described in the context of a 1.2micron CMOS process, but of course the process can readily be scaled ormodified, as will be apparent to skilled CMOS designers and processengineers.

The substrate 140, in this embodiment, is P-type silicon, doped to abulk resistivity in the neighborhood of 30-40 ohm-cm. The substrate isshown ohmically connected to ground through a shallow P+ diffusion 140A,but in addition to (or instead of) this contact, a backside contact mayalso be used for connection to ground.

An N-well 113 has essentially the same doping profile as the N-wellswhich are used to build PMOS active devices, and is formed in the sameseries of implantation and drive steps. In this sample embodiment, theN-well is about 4 microns deep, and has a vertically graded dopantconcentration in the neighborhood of 2-3×10¹⁶ cm⁻³. A shallow N+diffusion 113A is formed inside this region, by using the same implantas is used to form the N+ source/drain regions in the active deviceregions. This shallow N+ diffusion will normally be quite heavily doped,but the depth and concentration of this region are not particularlycritical for purposes of the structure of FIG. 16K. Typically theconcentration might be in the range of 1×10¹⁹ cm⁻³ to 3E²⁰ cm⁻³, with aneffective depth in the neighborhood of 0.3 microns. The shallow N+diffusion 113A provides ohmic contact to wiring 131, which iselectrically connected to the battery voltage V_(BAT).

An intermediate-depth P-type region 121 is formed inside the N-well 113.In the presently preferred embodiment, this is formed by implantingboron at an areal dose in the approximate range of 6×10¹³ cm⁻² to 1×10¹⁴cm⁻² at an energy of about 30 keV, but of course other doses or energiescan be substituted.

A shallow N+ diffusion 122 is formed inside the region 121, by using thesame implant as is used to form the N+ source/drain regions in theactive device regions. This shallow N+ diffusion will normally be quiteheavily doped, but the depth and concentration of this region are notparticularly critical for purposes of the structure of FIG. 16K.Typically the concentration might be in the range of 1×10¹⁹ cm⁻³ to3×10²⁰ cm⁻³, with an effective depth in the neighborhood of 0.3 microns.The N+ diffusion 122 makes ohmic contact to wiring 133, which is routedto provide the V_(DD) on-chip supply voltage for the active circuits onthe chip.

A shallow P+ diffusion 121A is also formed inside the region 121B, byusing the same implant as is used to form the P+ source/drain regions inthe active device regions. This shallow P+ diffusion will normally bequite heavily doped, but the depth and concentration of this region arenot particularly critical for purposes of the structure of FIG. 16K.Typically the concentration might be in the range of 1×10¹⁹ cm⁻³ to3×10²⁰ cm⁻³, with an effective depth in the neighborhood of 0.3 microns.The shallow P+ diffusion 121A provides ohmic contact to wiring 131,which is electrically connected to the battery voltage V_(BAT).

FIG. 16L shows a test structure which is similar to the device structureof FIG. 16K, and FIG. 16M shows test data for this structure. Inrecording this data, collector terminal (marked I_(C) in FIG. 16L) wasconnected to the emitter terminal (marked I_(E)). The battery was heldat a constant voltage V_(BAT) =3 V. The battery current I_(B) andsubstrate current I_(SUB) were measured as a function of the emittercurrent I_(E) drawn from the second region 122. Thus, two curves areshown in this log-log plot. Note that the substrate current I_(SUB)remains down in the noise level until the emitter current I_(E) becomesquite large. (This low value of the substrate current is highlyadvantageous.) At the point circled on the I_(B) curve, I_(E) =-2.512mA, and I_(B) =2.510 mA. At the point marked with an asterisk on theI_(SUB) curve, I_(E) =-2.512 mA, and I_(SUB) =-45 pA.

FIG. 16N shows a further alternative embodiment, wherein a diffusionstructure is connected to provide ESD protection for an I/O connectionof a battery-powered integrated circuit. Note that the region 122 is notconnected to provide a V_(DD) output, but instead is connected to aninput/output line 134. (The I/O terminal can also optionally beconnected to a transistor gate, for amplification of incoming datasignals, but this is not necessary.) The I/O line 134 is also connectedto be driven by an NMOS output driver 150. This transistor, as shown,includes a first source/drain diffusion 151, which is ohmicallyconnected to the I/O line 134, a second source/drain diffusion 152,which is ohmically connected to ground, and a gate 153 which can bedriven by a data-output signal DO-bar. (Of course, other devicestructures, such as additional ESD protection structures, can optionallybe combined with the structure shown.)

The structure of FIG. 16N, in the preferred embodiment, uses severalenclosure relationships in its geometry. The central diffusion 122 isshown small, for clarity, but may itself be large. The P+ diffusion 121Apreferably runs all around the P-type intermediate diffusion 121. Aspresently contemplated, lateral dimensions for this example are asfollows. (However, it must be understood that these dimensions areintended to be purely illustrative, and should not be strictly reliedon. These dimensions are included merely to help show the inventors'present views as to the best mode of practicing this embodiment of theinvention.) The N+ diffusion 122 is preferably separated from P+diffusion 121A by a minimum spacing of at least 3 microns (in a 1.2micron layout), and the ring diffusion 121A is preferably at least 5microns wide. The N+ diffusion 113A preferably runs in a ring all aroundthe edge of the well 113. The N+ diffusion 122 is preferably at least 5microns wide, and is separated from the P+ diffusion 122 by at least 3microns. The P+ diffusion 140B, in the substrate 140, preferably runsall the way around the outside of the N-well 113. The minimum spacingbetween P+ diffusion 140B and N+ diffusion 113A is preferably at least 3microns, and P+ diffusion 140B is preferably at least 5 microns wide.

The output transistor 150 is preferably surrounded by a ring 154 ofN-well, and this ring is tied to ground through a shallow N+ diffusion155 at its surface.

The structure of FIG. 16N has the advantage that, when a negativetransient appears on the I/O line 134 for any reason (such as electricalnoise on a line, or electrostatic discharge), most of the currentsourced to this negative transient will be taken from the junction 111,rather than from the output transistor. Thus, minority carrier diffusionto discharge the battery is minimized, and battery lifetime is notdecreased by such transient events. This advantageously provides asystem which is longer-lived and more reliable. However, when the I/Oline 134 is in its normal range of positive voltages (e.g. during normaloperation at TTL levels), the first junction in the diode structure willbe reverse biased, and will not load the line 134.

FIG. 16P is a log-log plot of data for the device structure of FIG. 16N.A controlled current sink I_(DQ) is applied to the I/O connection 134,and two current components are measured as a function of I_(DQ) : thecurrent I_(BAT) drawn from the supply voltage V_(BAT), and the currentcomponent I_(GND) drawn from the ground connection. At the point circledon the I_(BAT) curve, I_(DQ) =-10.00 mA, and I_(BAT) =18.15 microA. Atthe point marked with an asterisk on the I_(GND) curve, I_(DQ) =-10.00mA, and I_(GNSD) =9.982 mA.

In the structure measured in FIG. 16P, the effective area of the firstjunction 111 (which is protected by the second junction 112) isapproximately ten times that of the junction area in the outputtransistor 150 (which also can source current from ground). Thus, acurrent differential of about 10:1 might be expected, purely due to thegeometrical ratios. However, higher ratios (almost 100:1) are actuallyachieved. Thus, FIG. 16P shows that the ratio of ground-sourced currentto battery-sourced current is greater than 500:1 is achieved for a 10 mAload, and even higher ratios can be achieved at lower load currents.

ESD Protection Diode Layout

FIG. 16A shows the layout of the ESD protection diode, in the presentlypreferred embodiment. This diode has doping profiles as just describedwith reference to FIG. 16N. Note that the structure shown actuallyincludes two diodes in series: diode 618 provides the primaryprotection. Diode 619 is interposed between diode 618 and the substrate,to provide some additional protection. Note that the n+ pattern of diode619 is slightly different, to impose a longer current path. Thisprovides a slight series resistance between the power output and theactive circuits, which helps to isolate the active circuits from the ESDdischarges.

Note that the pattern shown includes rounded corners on the metal,n-well, and n+ patterns. These rounded corners help to reduce thegeometry-dependent electric field enhancement which would otherwiseoccur at corners.

It is contemplated that, for even greater ESD protection, it may bepreferable to narrow the width of the n+ diffusions in the diode layout.This would further reduce series resistance in the path of electrostaticdischarges.

The module of the presently preferred embodiment has been tested, andfound to withstand a 7000 V positive discharge, and to be capable ofwithstanding negative discharges greater than 10,000 V. (Under positivedischarges, data loss does not occur until 7000 V, and device damagedoes not begin to occur until 10000 V (one microAmp of leakage).Negative discharges cannot cause data loss or device damage untilvoltages greater than 10000 Volts (how much greater is not known.)

Operation

The implementation of data transfer operations, in the presentlypreferred embodiment, will now be described.

All communications to and from the token are accomplished via twophysical connections, the "Data" line, and the ground return line. Thereading and writing of token data is accomplished through the use oftime slots and a command word protocol.

Electrical I/O Relationships

The bus protocol is also designed to minimize the charge transfer out ofthe battery in the module. This is done by using an "open-collector"type architecture. The protocol has been specified so that the modulenever sources current to the data line, but only sinks current.

When a data module is in contact with a host system, the host systeminitially pulls up the data line. (The module also preferably contains avery high-impedance pull-down resistor at this node, but this is done,in the preferred embodiment, merely to avoid the risk of floatingnodes.) The host system initiates each stage of a data transferoperation by driving the data line low. The module detects this fallingedge, and one of several further events can then occur.

If the module is being read (as previously determined by overhead bits),the module, after seeing the falling edge which starts the cycle, eitherwill or will not turn on its NMOS pull-down transistor, depending on thevalue of the data bit being read at that cycle. When the NMOS pull-downis turned on, the module lets its preset timing period elapse, and thenturns off the NMOS pull-down. Thus, when the system wants to read fromthe module, it applies a falling edge, waits a short time to be surethat the module has received the falling edge, and then attempts to pullup the data line, using a pull-up resistor which cannot overpower theNMOS pull-down transistor in the module. After waiting a sufficient timefor the pull-up resistor to have raised the line to a high level (if theNMOS pull-down is off), the system tests the data voltage to ascertainthe data bit. The system then waits for the maximum time period of themodule delay to elapse, plus enough time for the data line to stabilizeat a high level, and then sends another falling edge to read the nextbit.

If the module is being written to (as previously determined by theoverhead bits), the module, after seeing the falling edge which startsthe cycle, waits for its preset timing period to elapse, and then storesthe logic value of the data line. Thus, when the system wants to writeto the module, it applies a falling edge, waits a short time to be surethat the module has received the falling edge, and then drives the dataline either high or low, depending on the data bit. The system thenwaits for the maximum time period of the module delay to elapse,restores the data line to a high level, allows enough additional timefor the data line to stabilize at a high level (and for the edgedetector in the module to reset itself), and then sends another fallingedge to write the next bit.

All Data Transfer operations are performed by initially setting thetoken into a known state, issuing a Command Word, and then performingthe selected operation, either reading the contents of the token orwriting new data into the token. Each Data Transfer operation consistsof 264 Data Time Slots: 8 are for the Command Word and 256 are for thedata bits.

To initially set the token into a known state, when a new token is firstinserted into a host system, either 264 or 1032 Write Zero Time Slotsare issued (depending on the memory density). These Write Zero TimeSlots will not corrupt the data held within the token since a CommandWord has not been written. This operation will increment the addresspointer internal to the token to its maximum count value. Upon reachingthis maximum value, the token will ignore all additional Write Zero TimeSlots issued to it and the internal address pointer will remain lockedat the top count value. (This backed condition is removed by the issuingof a Write One Time Slot.)

Once the token has been set into a known state, a Command Word istransmitted to the token, using 8 Write Data Time Slots. This resets theaddress pointer internal to the token and prepares it for theappropriate operation, either a read or a write.

After the Command Word has been transmitted to the token, theappropriate number of Data Time Slots will be issued to the token by thehost. In the case of a read operation, these will be Read Data TimeSlots. In the case of a write operation, these will be Write Data TimeSlots. The exact number of Data Time Slots generated by the host isdependent upon the memory density of the part being used (256 or 1024).

Block Transfer

All data transfers are preferably done by reading or writing the entirecontents of memory as a single serial stream.

Overhead Bits

A command word, which is a short block of overhead bits, is sent fromthe host system to the portable module at the start of each transfer, todefine the transfer type. FIG. 4 shows the organization of the overheadbits which are used in each block transfer.

The Command Word consists of 8 bits which are transmitted from the hostto the token with write data time slots (FIG. 4). The first bit of theCommand Word must be set to a logic 1 level. The next two bits are theSelect Bits which relate to the part dash number. The remaining fivebits determine whether a read or a write operation is to follow. If awrite operation is to be performed, all five bits are set to a logic 1level. If a read operation is to be performed, any or all of these bitsare reset to a logic 0 level. Each of these bits is transmitted to thetoken with a separate write data time slot.

Address-Pointer Reset

When a host system first makes contact with a module, the host systemsends a long string of write-zero commands, followed by a write-onecommand, to the module. The module contains a counter, which monitorsthe incoming bit stream for nonstop sequences of write-zero commands. Ifthe module receives a nonstop sequence containing as many write-zerocommands as the total length of the memory, the counter will freezeuntil the chip is reset. The chip will be reset if and only if anincoming "1" bit is seen while the counter is frozen.

That is, in the presently preferred embodiment (256 bits of memory), thedata output of the last counter stage (indicating that the counter hasrolled over from 255 to 256) triggers a flip-flop whose output isconnected, through a NOR gate, to cut off the counter's clock input.

This provides a reset capability, whereby the system can ensure that thestarting address of the module is accurately known. Thus, on everyinsertion of a new module, the system can send such a reset sequence toinitialize the address pointer in the module. Note that thisaddress-pointer-reset is only necessary once per insertion. The sequenceof write-zero commands will not normally destroy data, because themodule never receives the overhead bit sequence which would tell it toenter write mode. (The only conditions under which data could bedestroyed by these commands is when the module has been interrupted inthe middle of a previous write sequence, and in this case the data maybe presumed corrupt anyway.)

Read/Write Timing

There are two types of write data time slots, Write One Time Slots andWrite Zero Time Slots. A write data time slot is initiated when the hostpulls the Data line from a high logic level to a low logic level. Allwrite data time slots must be a minimum of 60 microseconds in durationwith a minimum of 1 micro-second recovery time between write cycles. Inthis example, the crude time base in the module provides a 4:1 range inthe possible time durations: timing relations are defined with respectto a one-shot in the module which will provide a pulse width of at least15 microseconds (but not more than 60 microseconds).

This one-shot is preferably trimmable, to a wide variety of speedranges. Moreover, other circuit arrangements could be used instead, togenerate a timing base. Thus, in the following example, the timingwindow of 15-60 microseconds does not delimit the claimed inventions,but merely serves to illustrate how the one-wire bus protocol can copewith timing uncertainty. The same principles of operation could be usedif the modules were trimmed to have varying time delays within the rangeof (for example) 1-4 microseconds.

FIG. 2A is a timing diagram of a write-1 operation, in the module of thepresently preferred embodiment. For the host to perform a Write-1operation, the following steps occur:

1. The Data line is held at a high level for at least one microsecond.This ensures that the edge detector in the module will have sufficientset-up time.

2. The Data line is pulled to a logic low level. This provides thefalling edge which the module uses to time its operations from.

3. The Data line is then held low for at least one microsecond, toensure that the falling edge is detected by the module.

4. After the falling edge, the Data line must be driven high within 15microseconds, and held high for at least 60 microseconds (from the timeof the falling edge in Step 2). This ensures that the Data line will behigh when the pulse generated by the one-shot in the module ends. Whenthe pulse ends (producing a falling edge), the module will sample thelogic level of the data line, to determine whether a 0 or a 1 is thedata value.

Steps 1-4 can then be repeated, to write the next bit.

FIG. 2B is a timing diagram of a write-0 operation, in the module of thepresently preferred embodiment. The steps in this operation are the sameas the steps in a Write-1 operation, except that, in step 4, the Dataline is held low during the window of 15-60 microseconds after thefalling edge. This ensures that the Data line will be low at the end ofthe pulse generated by the one-shot in the module.

FIG. 3 is a timing diagram of a read operation, in the module of thepresently preferred embodiment. When data is to be read from the tokenby the host, the host will generate the read data time slots. A readdata time slot is initiated (as in steps 1-3 of the write-1 operation)when the host pulls the Data line from a logic high level to a logic lowlevel. As soon as the module sees this failing edge, it willconditionally turn on its pull-down transistor (depending on the valueof the data bit being read), and will leave the pull-down transistorturned on (conditionally) until the end of the pulse generated by theone-shot. Thus, during a read operation, after the falling edge (and thefollowing guard time), the host waits for enough time for the data lineto have been pulled up to a high level (if the module is not holding itdown), and then samples the data line. In the presently preferredembodiment, where the host port has a 5 Kilohm pull-up resistor, thehost preferably tests the data line 10 microseconds after the fallingedge. From 15 to 60 microseconds after the failing edge, the state ofthe data line is uncertain, since it is not known whether the module hasyet timed out and released the data line. All read data time slots mustbe a minimum of 60 microseconds in duration, with a minimum of 1micro-second recovery time between read cycles.

The module's time base varies widely between parts, and may also bequite dependent on temperature (which will typically vary the batteryvoltage). However, the module's time base will not vary as widely frommoment to moment. Thus, in a less-preferred alternative embodiment, thehost can measure the time base of the module (by performing morefrequent samplings during a read operation), and maximize the data ratefor the particular module being read. However, this is not preferred,since the most preferred system embodiment will typically have onlybrief exchanges (one read, or one read plus one write) in each contactof a host with a particular module.

System Using Electronic Tokens

These ideas are used as pans of a very system architecture. Theelectronic module enabled by the teachings herein is extremely compactand extremely cheap. From a systems point of view, this module is insome ways more analogous to a read/write bar code than to a conventionalelectronic memory system.

Thus, this module can be used for price tags, for inventory tags, forwork-in-process monitoring, for retail sales (to permit customers toselect merchandise (e.g. by taking one module or a handful of modules toa cashier or to an automated checkout machine), without exposing theactual inventory to pilferage), and for a wide variety of other suchcompact data-transfer applications. Thus, the module described can beregarded as an electronic token, which is as portable and rugged as ametal token, but which is far more versatile.

Host System

An electronic token can be interfaced to by an open-collector pin in avery wide variety of microprocessors. Moreover, some port pins on somemicroprocessors have very weak pull-ups, so that these port pins couldalso be used. Alternatively, a microprocessor which did not have anysuch pins available could buffer its port through a standard TLopen-collector buffer.

It is particularly advantageous to interface a token receiver to astandard microcomputer system, such as an 80286- or 80386-based PCclone.

FIG. 12 shows a simple example of a host system, which can interface toelectronic token modules like the module of FIG. 1. In this example, thetoken data line is taken from an open-collector pin of a microprocessor(such as a Motorola 68000). A 5 kilohm resistor 1204 provides a pull-upto V_(CC), and an open-drain driver 1202 amplifies transmitted signals.

Other sample embodiments of the host system will be discussed below,with reference to FIGS. 19 and 20.

Physical Interface for Receiving Electronic Tokens

Preferably each host system uses a physical configuration of electricalcontacts which provides rapid contact for electronic data modules(tokens). A slot, dimensioned to receive electronic tokens, includes agrounded contact positioned to make contact to the edge of a token whichmay be inserted, and two data contacts which are positioned to makecontact to the opposite faces of the token. Each of the data contacts isconnected to an open-collector driver circuit, including a pull-upresistor which will bring the potential of the contact high when theslot is empty. The token is shaped so that its edge, and one of itsfaces, are connected to the token's ground line, and the other face isthe token's data line. Thus, when a token is inserted (no matter whichway the token is facing), one of the two data contacts will beimmediately pulled to ground, by short-circuiting across the groundplane of the token. The system can thereby recognize that a token hasbeen inserted, and that the other data contact (the one which was notshorted to ground) can communicate with this token's data line. Thus,even though the token itself is asymmetric, and even though thedirectional orientation of the token is not initially known to thesystem, no physical asymmetry needs to be introduced into the token orthe slot to assure proper data interface.

FIG. 17 shows the configuration of contacts used, in one embodiment, ina host system to contact electronic tokens. A slot 1720 in a body 1710is dimensioned to accept a token (e.g. like the tokens of FIGS. 1A or1B). Contact 1736, in the bottom of the slot 1720, is positioned tocontact the edge of an inserted token. Contacts 1734 and 1732, onopposite sides of the slot 1720, will contact the two opposite faces ofthe token.

Thus, when a token like that in FIG. 1 is inserted into a slot like thatof FIG. 17, contact 1736 will always contact case portion 0100B. Caseportion 0100B will also contact one of the other contacts 1732/1734, andpull it to ground. Thus, when a token is inserted, the host system willsee one of the data lines DQ1/DQ2 pulled to ground. This tells the hostthat a token has been inserted, and it also tells the host which of thetwo data lines DQ1/DQ2 the token's data lead is connected to. (Thetoken's data lead will be found connected to the data lead which was notpulled to ground.)

Alternative Physical Interface--Hand-Held Wand

In an alternative embodiment, a wand provides rapid contact to atwo-terminal electronic token data module. The wand includes one contactwhich will make contact to the periphery of an electronic token whichthe wand is pressed against, and one contact which will make contact tothe center of the token. Preferably the wand includes a base portionwhich is shaped to be worn on the second joint of a user's finger. Thiswand can be used for very rapid manual contacting of electronic tokensin various physical positions. This can be very advantageous in avariety of data collection/updating applications such as retailcheckout, or tracking work-in-progress in acomputer-assisted-manufacturing environment.

FIGS. 15A, 15B, and 15C show the finger-mounted wand used, in thepresently preferred system embodiment, for manually contacting multipleelectronic tokens successively. This wand is particularly suitable forcontacting tokens which are firmly affixed to solid items, forapplications such as workpiece identification in computer-integratedmanufacturing, or inventory control, or equipment maintenance records.

FIGS. 15B and 15A shows the top portion 15 10 of the wand of thepresently preferred embodiment. The entire structure shown, except forconductive ring 1518, is preferably molded from a non-conductivepolymer. A lip 1516 surrounds a recess which is dimensioned to mate withtokens of a known dimension. A thin ring of conductive polymer 1518circles the inner edge of the lip 1516. This ring will make the actualelectrical contact to the edge of a token. The ring 1518 providessufficient elastic deformation to assure that secure contact is made. Athrough-hole 1502 in the center of the recess carries a wire (not shown,for clarity) which contacts the center of the token when contact ismade. FIG. 15A shows the back side of the top portion 1510. Note thatanother through-hole 1504 permits a second wire (also not shown) tocontact the backside of conductive ring 1518. A groove 1514 permits thetwo wires to be led out, for connection to a host computer system.

FIG. 11. 15C shows the finger-mounted base portion 1590, whichpreferably is cemented (or otherwise attached) to a top portion 1510,like that shown in FIGS. 15A and 15B. The fiat surface 1592 is attachedto fiat surface 15 12 on the top portion 1510. Aperture 1594 is shapedto fit a user's finger. Preferably this is shaped to fit the secondjoint of the user's finger, unlike normal ting sizing, where the ring isplaced on the first joint of the finger (nearest the palm).

Thus, the complete structure is compact, and can be easily worn on theuser's finger without interfering with other activities. The lead wirescan be connected to, for example, a belt-mounted small data-holdingcomputer unit, or to a belt-mounted RF interface unit.

Electrical Interface from Host System

The host system must have an open drain driver with a pull-up resistorof approximately 5 Kilohms to V_(CC) on the Data signal line. The tokenhas internally an open drain driver with a 500 Kilohm pulldown resistorto ground (FIG. 6). The open drain driver allows the token to be poweredby its small internal energy source and still have the ability toproduce sufficiently large voltage swings at the outputs. The pulldownresistor holds the Data input pin at ground potential when the token isnot connected to the host.

FIG. 18 shows the electrical driver configuration used on the host side,in one class of embodiments, to interface to electronic tokens. Twoopen-collector interfaces are provided, 1810A and 1810B. The data lineDQ₁, from a contacting fixture (e.g. like that shown in FIG. 17) isconnected to one of the interface circuits 1810S, and the other dataline DQ₂ is connected to the other interface circuit 1810B.

When the host system has not been communicating with a token, it cansimply poll the XOR value the two data input lines DI₁ and DI₂ to testfor the presence of a token. When a token has been inserted, the hostcan begin to drive the DQ line which was not pulled low by the insertionof the token. As discussed below, the host would normally issue a resetsequence, read the memory, and then (in some cases) write the memory.

Electrical Interface from Token to Standard RS232 Interface

The presently preferred embodiment also uses an electrical interface tothe tokens, which permits interfacing to tokens with a wide variety ofcomputers, including a tremendous variety of personal or othercomputers, as long as the computer includes an interface to RS232 (orsome comparable standard). The token has a one-wire-bus interface,implemented in a battery-backed open-collector architecture, whichprovides a read/write interface. The communication protocol expected bythe token has been specified so that the token never sources current tothe data line, but only sinks current. The communication protocol alsoincludes time-domain relations which are referenced to a very crude timebase in the token, and the system must preserve timing relations whichwill be satisfied by tokens in which the time base takes on any of thewide range of foreseeable speeds. To interface to this protocol, theprogrammable capabilities of the standard UART chip in the computer'sRS232 interface are exploited to provide adaptation to the time baserequirements of the module. This is done by writing an entire byte ofoutput from the UART, at a much higher baud rate than the module can berelied on to accept, to write a single bit of data into the module. Theread-data line (RX) of the UART is tied back to the transmit-data line(TX) through a resistor, so that the UART will also always report a readof the same data byte being written, unless the token has turned on itspull-down transistor. An electrical network is used at the interfacewhich (in effect) reverses the ground plane identification of the twoleads, but which does provide the correct signal polarity to the tokenfor signal discrimination in read mode.

FIG. 19 shows a network used, in the preferred version of thisembodiment, to interface from a serial port to an electronic token. Dataline 1900A contacts the data terminal 0100A of a token, and ground line1900B contacts the ground terminal 0100B of a token.

The example shown provides an interface to a standard PC's serial port.Lines RTS (pin 4) and DTR (pin 20) are used for a power supply in thisembodiment, but either of these pins could optionally be used aloneinstead. When interfacing to a token, lines DTR and RTS are driven to apositive voltage level, Zener diode 1910 holds the data line 1900A to aconstant potential at all times. In the presently preferred embodiment,Zener 1910 is a 5 V Zener.

The serial data out pin TX (pin 2) is used, with a series resistor 1912,to modulate the ground line 1900B which is connected to the groundcontact 0100B of the token. The serial data in pin RX (pin 3) is used toreceive data from the ground line 1900B. Thus, the token is in effectconnected backwards.

Schottky diodes 1910 and 1914 clamp the excursion of the ground line1900B. (These diodes can be implemented as a single 3-pindouble-Schottky-diode package.)

The reversed connection of the token turns out to be surprisinglyadvantageous. All of the RS232 interface chips presently on the marketprovide a trip point voltage of about 1.5 Volt (with about a half Voltof hysteresis). (This is not part of the formal RS232 specification,which simply defines the voltage range from -3 V to +3 V as a "deadzone".) Thus, this reversed connection, and the DC offset, assures thatthe modulation effected by the token module will fall into a rangearound the line receiver chip's trip point.

Software for Interfacing from Token to Standard UART

The TX and RX signals referred to above will normally by translated by aline/driver receiver chip (which converts the voltage levels to normallogic levels), and will then be connected to a universal asynchronousreceiver/transmitter (UART) chip.

Such UART chips are a widely used commercial part. They include logic toperform low-level signal formatting and manipulation, and byte-wideserial/parallel conversion of data streams. One example of a commonlyused UART chip, suitable for use in the embodiment of FIGS. 19 and 20,is an Intel 8250. However, a wide variety of other chips could be usedinstead.

UARTs are normally programmable, for parameters such as number of bits,baud rate, etc. Since each UART contains its own time base, timingparameters can specified to the UART without considering what the speedof operation of the overall system may be. (For example, the PC-typesystems currently in widespread use range from XTs operating at 4.77 MHzto 80386 systems operating at 33 MHz.) In the presently preferredversion of this embodiment, the serial data lines are interfaced to aUART which has been programmed for operation at 115 kilobaud, with 1start bit, 6 data bits, and 1 stop bit per byte. However, theseparameters can readily be varied: for example, even without changing thespecific timing parameters of this embodiment, the number of data bitscan be increased to seven or eight or more without causing any problems.

FIG. 20 shows timing relations preferably used, in a sample embodiment,for interfacing from a standard RS232 port to an electronic token toperform a Write-0 operation. (These timing diagrams show signals withreference to the token's ground terminal, which, in this embodiment, isnot the same as system ground.) When the UART sends a start bit, thetoken sees the falling edge which starts its time window. The startbit's time slot guarantees that the line level will be held low for 8.68microseconds after the falling edge. Thereafter, the 6 data bits (allset to zero) keep the signal level low, from 8.68 microseconds after thefalling edge until 60.764 microseconds after the falling edge. Thus,whenever the one-shot pulse ends, and the token samples the data line,it will see the desired data value. This is achieved by writing anentire byte of output for each bit desired. After the data bits, thestop bit provides a high level for 8.68 microseconds, which is more thanlong enough to reset the edge detector n the token.

A write-1 operation is almost the same as the write-0 operation, exceptthat the data bits are all 1s (rather than all 0s).

The resistor 1912 means that signals driven onto the TX lie will beechoed on the RX line. This permits a simple read operation. After thetoken has been set into read mode, the host writes a byte of all 1s. Atthe same time, the receiving side of the UART will be receiving a byteof data. If the first received data bit is a zero, the host knows thatthe module has turned on its pull-down transistor. If the first receiveddata bit is a one, the host knows that the module has not turned on itspull-down transistor. The remaining data bits are ignored, since even ifthe pull-down transistor was on, the module may already have turned itoff at any time after 15 microseconds past the falling edge.

Source Code--Software Interface

In the presently preferred embodiment, the following code is used todrive the serial interface to a token. In this listing, "TBE" means"Transmit Buffer empty"; "TSRE" means "Fransreit Shift Register Empty,"i.e. no data is currently being sent; "RDA" means "Received Data isAvailable," i.e. the receiver side of the UART is holding some data.

Thus, to perform a read operation, the host writes out hexadecimal byteFF_(H) (or 3F_(H) --with only six bits the two numbers appear the same.The first data bit in a byte is conventionally taken as the leastsignificant bit. Therefore, the received data byte can simply be testedto see whether it is odd or even. ##SPC1##

Design Considerations

Since the token is designed to be used as a removable tagging device, itcan be viewed at the system level as a memory element plagued bynumerous cold solder joints. During either reading or writingoperations, physical contact with the token may be broken. This in turnwill cause either the received data to be erroneous or the transmitteddata to be incomplete. The recommended way around these problems is asfollows:

1) Read Operation

step 1--set token to a known state

step 2--issue a read Command Word

step 3--read the data into host memory

step 4--repeat steps 1 through 3 five times

step 5--use majority wins logic to derive data (i.e. 3 out of 5 wins)

2) Write Operation

step 1--set token into known state

step 2--issue a write Command Word

step 3--write data into token memory

step 4--perform Read Operation

step 5--compare host transmit data to received data

step 6--if not, equal, repeat steps 1 through 5.

Further preferred embodiments

Further preferred embodiment circuitry for chips 0130 and 0130' in themodules of FIGS. 1A-B are shown schematically in FIGS. 21, 22A, 22B,22D, and 22G. FIG. 21 is a top level schematic of the embodiment,denoted generally 2100, which includes a single input-output terminalIO, a 1-wire converter 2102, an 8-bit command shift register 2104, acommand decoder 2106, ROM and control 2108, secure RAM 2110, multiplexer2112, power supply battery 2114, and battery test circuit 2116.Embodiment 2100 receives and transmits serially over the IO terminal aspreviously described in connection with FIGS. 2A-B and 3: converter 2102receives input (low pulses) at IO through buffer inverters 2120 andtransmits output to IO by applying low pulses to NAND gate 2122 whichturn on n-channel transistor PLDWN to pull down IO and generate lowpulses. Converter 2102 translates between input and output at IO andfour synchronous signals CLOCK, DATA₋₋ IN, DATA₋₋ OUT, and ENABLE foroperation of 2100.

The overall operation of embodiment 2100 follows a three layerhierarchical procedure: in the first layer the host sends a resetcommand by holding the IO node low for at least 480 microseconds andthen returning IO to high for at least 480 microseconds. This causesembodiment 2100 to generate a presence detect signal by pulling node IOlow for at least 60 microseconds as described below in connection withFIG. 22F. The reset command also clears the command register 2104 andsets the module in a mode for the host to write a byte (8 bits) intocommand register 2104 in the next eight write cycles as illustrated inFIGS. 2A-B and described below in connection with FIGS. 22B-E. Oncecommand register 2104 is loaded with a command byte, command bytedecoder 2106 decodes the command byte to initiate one of the fourallowed commands: READ ROM DATA, MATCH ROM DATA, SEARCH ROM DATA, andSKIP ROM SECTION of the second layer. (If the byte in command bytedecoder 2106 fails to match one of the available commands, then themodule will simply wait for a reset and ignore further commands at itsinputs.) These commands employ identification data from the ROM in 2108and incorporate the security aspects of the module. The upper portion ofFIG. 23A illustrates the flow. Then after successful execution of thesecond layer command, the third layer commands are available for accessto the secure RAM 2110. The lower portion of FIG. 23A shows theexecution of these third layer commands. Note that the flow paths allend in a reset. Also, the second layer commands dealing with the 64 bitROM in 2108 may have simple hardware support in that the entire 64 bitsare always read or compared, so the addressing can be a simpleincrementing with the successive comparisons just fed to a latch thatswitches if a mismatch occurs. The following preferred embodimentdiscussions explain these commands and variations in detail.

FIG. 22A shows decoder and ROM 2108, and FIG. 22G shows register 2104and decoder 2106; both Figures are discussed below. FIG. 22B shows themain portion of converter 2102 which is a state machine and oscillatorwith input node IOT, interrupt input node INT, power-on-reset input nodePOR, output node IOPULDWN, input internal data node DIN, output internaldata node DOUT with adjacent latch made of cross-coupled NOR gates 2233and 2234, internal clock output node CLK, status input node READ,internal reset output node RSTB, oscillator TPOSC, RC delay circuit DSMfor timing in the state machine, and state machine 2200. State machine2200 occupies most of FIG. 22B and includes cross-coupled NOR gatelatches 2208-2214, eight input lines labelled GT60, IOB, IOT, GT5, GT20,GT8, GT1B, and GT1 (lefthand eight vertical lines in the center of FIG.22B), ten feedback lines labelled B4, B4B, B3, B3B, . . . B0, and B0B(the fighthand ten vertical lines in the center of FIG. 22B), and sundryNAND and inverted input AND gates from the eighteen input and feedbacklines to the latches. B4B is the complement of B4, B3B is the complementof B3, and so forth. Note that the inputs to the eight input lines arenode IOT (to line IOT) and its complement (to IOB) and six timingsignals from oscillator TPOSC: GT1, GT1B (complement of GT1), GT5, GT8,GT20, and GT64. FIG. 22C shows the relation of these timing signals tothe oscillator's clock which is presumed enabled at time t₀ ; the periodof the oscillator's clock is about 60 microseconds. Thus GT1 goes highafter one period (60 microseconds) and stays high, GT5 goes high afterfive periods (300 microseconds) and low after six periods and again highafter seven periods and so forth, GT8 goes high after eight periods (480microseconds) and low after sixteen periods and so forth, GT20 goes highafter twenty periods (1.2 milliseconds), and GT64 goes high aftersixty-four periods (3.84 milliseconds).

FIG. 22D is a schematic circuit diagram of oscillator TPOSC whichincludes a latch of cross-coupled NAND gates with two feedback loops ofinverters with each loop having a resistor R and capacitor C to generatean RC delay which essentially sets the length of each half period ofoscillation (about 30 microseconds). The RC exponential voltage decaycauses the inverter to switch at approximately half the supply voltageand thus the delay for each phase is voltage supply independent andequals RC(ln2). The oscillator is a two phase oscillator and the RC timereference is relative to ground in one phase and to VDD in the other.This provides some degree of process insensitivity to variation in MOSthresholds and transconductances. Process variations between n-channeland p-channel devices cause the inverters to switch at some voltage Vswnot exactly equal to VDD/2. The circuit is such that if in one phase thevoltage must swing greater than half the supply voltage in the alternatestage it will swing less. This accomplishes the desired stabilization ofoscillator period to process variation.

The resistors can be laser trimmed during manufacture to insure areasonably close to 30 microsecond half period. The oscillation outputof the latch drives counter COUNTER made of seven flip-flops: eachsuccessive flip-flop clocks at half the rate of the preceding one. TheGT1, GT5, GT8, GT20, and GT64 signals simply tap off of COUNTER in thestandard manner except GT1 also has a NOR gate latch driven by COUNTER.Additionally, the input node EN connects to the NAND gate latch, thereset inputs of the flip-flops and the GT1 latch. A low at input node ENdisables the oscillations, resets the counter to all zeros and forcesthe GT1 latch to make GT1 low; whereas, a high at node EN permitsoscillations and counting by the counter and the GT1 latch to switch tomake GT1 high after one oscillation period. Note that the GT1 latchholds GT1 high until a disabling of TPOSC by a low on node EN.

The operation of the state machine 2200 of FIG. 22B could be explainedby tracing through all of the possible states: the five latches2210-2214 set the ten feedback lines B4, B4B, . . . B0, B0B, so therewould be 2⁵ possible states. (Latch 2209 only outputs to node RSTB andlatch 2208 only outputs to the EN input of oscillator TPOSC.) Such ananalysis would generate a state diagram which reveals that the statemachine is gray coded (only one latch switches at a time) and that thereare only four stable states. However, for simplicity and clarity justconsider the state diagram FIG. 22E wherein each state is represented bya rectangle with a 5-bit binary number showing the high or low of linesB4, B3, . . . B0 (the outputs of latches 2214, 2213, . . . 2210,respectively) and the transitions between states that require an inputare represented by the decision rhomboids. Note that many of thetransitions are induced by timing signals from oscillator TPOSC. Forexample, RESET IDLE state 00000 (rectangle in the top center of FIG.22E) has B4=B3=B2=B1=B0= 0 and this implies that NAND gate 2220 is low(due to B3B=B2B=B1B=BOB=1) which, along with B4 low, drives invertedinput AND gate 2221 high, thus NOR gate 2222 low, then NAND gate 2224high, and hence latch 2208 outputs a low to input EN of oscillatorTPOSC. EN low turns off and resets TPOSC so input lines GT1, GTS, GT8,GT20, and GT64 all remain low. Of the possible 32 states only 18 areused and all other states are collectively decoded as "badstate". If anybad states are detected the state machine is forced into a particulargood state, the reset state (10001). This prevents the state machinefrom becoming permanently locked into a bad state. Furthermore moststates are transitory in nature and even without any external activitywill transition to a new state within a finite time. The only stateswhich are stable are ACTIVE IDLE (10010), RESET IDLE (00000), RESET(10001), and ALARM RECOVERY (10111). In each of these stable states theoscillator is shut off and the circuitry only consumes leakage currentfrom the battery. The first two of these states are stable if IOT isheld high while the latter two only if IOT is held low. Typically, IOTwill be internally pulled low by a weak pulldown (e.g., FET 2130 in FIG.21), so that a disconnected device is automatically held in the RESETstate. The state 00000 is stable provided input node IOT is high (solines IOT=1 and IOB=0) and input node INT ("interrupt" or "alarm") islow, and this is the reset or inactive state for the state machine whenthe host is not communicating with the module. Now two different inputswill cause a state change as indicated by the two decision rhomboids onthe outgoing lines from rectangle 00000: namely, (1) IOT going low whileINT remains low and (2) INT going high. The operation of the statemachine for these two inputs is as follows:

If the host applies a low signal at input node IO (see FIGS. 2A-B and 3and related discussion above) when the state machine is in state 00000,this drives input line IOT low (and line IOB high) which switches latch2214 to yield the state 10000 as indicated in FIG. 22E by the IO/ALARMdecision rhomboid with IO=0 and ALARM=0 output going down to Activestate 10000 from upper Inactive state 00000. State 10000 drives latch2208 to output a high to the EN input of oscillator TPOSC and therebyturn on TPOSC. Thus the timing signals GT1, GT5, GT8, GT20, and GT64begin as shown in FIG. 22C, although for a read or write, TPOSC isdisabled just after one or two periods and only in response to a resetsignal from the host do GT5, GT8, or GT20 ever go high. In particular,consider the possible cases as follows.

First, presume that READ =0 and the host applies a low signal that lastsabout 10 microseconds and then returns to a high; this would be thesituation for a write of a 1 as illustrated in FIG. 2A. In this case theinput IOT returns high prior to GT1 going high, and NAND gate 2225 goeslow to switch latch 2213 and put state machine 2200 into state 11000;see the lefthand portion of state diagram FIG. 22E. Also, latch 2213switching high makes NAND gate 2228 go low and, because NAND gate 2229is low, inverted input AND gate 2238 high to thereby drive CLK node low.This is the clock output of converter 2102. Next, after GT1 goes high (amaximum of 60 microseconds after the host had first driven the inputnode IO low), NAND gate 2227 goes high and switches latch 2211 to yieldstate 11010 which also drives NAND gate 2229 high and thus invertedinput AND gate 2238 low and thus CLK output high again. But state 11010drives NAND gate 2230 high and thus latch 2213 switches to put statemachine 2200 into state 10010 (upper lefthand portion of FIG. 22E)because IOT is high. State 10010 switches latch 2208 to turn offoscillator TPOSC, and state machine is in an active idle state waitingfor the host to drive lOT low for the next cycle; see FIG. 2A. Note thatwhen state machine 2200 switched to state 11000, the latch 2233-2234switches to have DOUT high (write a 1), but inverted input AND 2238returning low does not switch latch 2233-2234 and DOUT remains high whenCLK returns high. Also, the enable (CMDRST low) for command register2104 is activated, so this 1 at DOUT appears at input node CMDDATA andloads into the first flip-flop of command register 2104. See FIG. 22Gwhich shows both command register 2104 and decoder 2106. Note that upona reset signal (a high at input node CMDRST) all of the flip-flops ofregister 2104 reset to Q=0 except the first flip-flop which sets to Q=1.As successive writes fill up register 2104, the initial 1 in the firstflip-flop propagates through the the other eight flip-flops until thelast flip-flop loads it and thereby stops the further clocking ofregister 2104 and activates decoder 2106 by releasing the output NANDgates from their fixed highs.

Second, presume that the host applies a low signal that lasts about 100microseconds and then returns high; this would be the situation for awrite of a 0 as illustrated in FIG. 2B. Again the low at IOT firstswitches the state machine into the 10000 state (either from the resetidle state 00000 or the active idle state 10010) and starts oscillatorTPOSC. But in this case GT1 goes high (a maximum of 60 microsecondsafter TPOSC is enabled) prior to IOT returning high, and thus the statemachine switches into state 10100 rather than state 11000 when IOTreturns high. Again, the switch of states when IOT returns high drivesCLK low, but by making NAND gate 2231 low which drives inverted inputAND 2239 high and thus CLK low plus switches latch 2233-2234 high todrive output node DOUT low (write a 0). The switching output of invertedinput AND 2239 to high also drives delay circuit DSM which after a delayof about 1000 nanoseconds switches latch 2211 to put state machine 2200into state 10110 (see hexagonal block near center of FIG. 22E) and thisreturns CLK high and switches latch 2212 to put state machine intoactive idle state 10010. Thus the delay circuit DSM sets the CLK lowpulse duration. Of course, CLK making the low-to-high transition clockscommand register 2104 and loads the 0 at DOUT into the first tip-flop.

Third, presume that the host applies a low signal that lasts about 10microseconds and then releases terminal IO in order to read a 0 or 1 asdescribed in FIG. 3. Again, IOT going low switches state machine 2200into state 10000. Then node READ high implies an immediate switch intostate 11000; see the lefthand portion of FIG. 22E. This is similar tothe situation for a write of a 1 described previously, and again gate2238 goes high to drive CLK low and also supplies a high to NAND gate2248. Node READ high is another high input to gate 2248; then if thesignal at node DIN is low (as read a 0), this provides the third high togate 2248, and gate 2248 is low which drives node IOPULDWN high to turnon pull down transistor PLDWN to pull down terminal IO which the hostcan sense as a low. Contrarily, if the signal at node DIN is high, thengate 2248 is high and node IOPULDWN remains low and node IO is notpulled down so the host can sense a high. The distinction between readand write (node READ high or low) derives from the command in 2108 orRAM 2110 outside of state machine 2200. Note that if READ is low, thengate 2248 is held high and does not drive IOPULDWN, so the data from RAMor ROM (depending upon the command in register 2104) at input node DINis just ignored.

Note that IOPULDWN can also be activated to pull down terminal IO byeither of inverted input AND gates 2262 and 2264 being high. Now gate2262 is high precisely when state machine is in the states 0001x (thatis, 00010 or 00011), and gate 2264 is high precisely when state machineis in the state 10101. These states correspond to alarm and presencedetect states described in the following.

Lastly, presume that the host applies a low signal that lasts more than480 microseconds; that is, long enough for GT8 to go high. In this case,IOT going low again puts state machine 2200 into state 10000 and startsTPOSC. But IOT remains low until GT8 goes high which switches statemachine 2200 into reset state 10001 (center portion of FIG. 22E) whichturns off TPOSC. Then when IOT returns high state machine 2200 switchesinto state 10011 and restarts TPOSC, and GT1 going high (after about 60microseconds) now switches state machine 2200 into state 00011 and thishas both NAND gates 2242-2243 high which, in turn, drives node IOPULDWNhigh to turn on transistor PLDWN for the presence detect signal. Thepresence detect signal persists until GT5 goes high to switch statemachine 2200 into state 00001 and then back into either reset idle state00000 if IOT is high or reset state 10001 if GT20 goes high while IOT isstill low. Note that this GT20 test assures that a module which isdischarged to ground at its IO terminal will eventually enter the resetstate and always issue a presence detect signal. Also, note that ifmodule 2100 is not connected to a bus, then the internal weak pulldownFET 2130 will make IO low and module 2100 is self resetting.

FIGS. 22H-22N are simulated timing diagrams for the write and readoperations plus resets in the midst of write and read operations plus aself reset.

State diagram FIG. 22E also shows an alarm/interrupt branch of operationthat begins with a high on input node INT in FIG. 22B. A high on nodeINT makes NOR gate 2252 go high (presuming pending alarm latch 2250 ishigh as is the case for state 00000)which drives NAND gate 2254 high andthis leads to latch 2211 switching to put state machine 2200 into state00010. This starts TPOSC and when GT64 goes high state machine switchessuccessively from state 00010 to state 00110 to state 00111 to state10111 as illustrated in the righthand portion of FIG. 22E. As notedpreviously, state machine 2200 in state 00010 implies a pull down ofterminal IO; and as seen in FIG. 22E, state 00010 persists until GT64goes high, that is an alarm signal is generated by pulling down terminalIO for about 3.84 milliseconds. Note that the other branch of alarmstates beginning from the reset state 10001 (near the center of FIG.22E) stays in alarm state 10101 (which also pulls down terminal IO aspreviously seen) until GT64 goes high.

For a one-wire multidrop system (that is, multiple modules on a 1-wirebus with a bus master host) supporting interrupts a particular concernis the collision of interrupts with either other interrupts or normalcommunication. Several interrupt priority schemes are possible and inthis implementation normal communication is given priority overinterrupts. Hence the state machine 2200 is designed such that anasynchronous interrupt will not corrupt an ongoing one-wirecommunication. There are two states from which a latched interruptsignal ALARM can cause state transitions. The first is the RESET IDLEstate 00000 which is the normal idling condition of a system that wishesto enable interrupts. This state is entered after a reset and presencedetect and allows interrupts to be issued as soon as they occur. Aspecial one time only signal (OTA at NOR gate 2252) is used to serviceinterrupt request from the RESET IDLE state. This is necessary becausethe module will eventually return to this same RESET IDLE state. Inorder to prevent a module from continuously issuing its alarm in a neverending cycle this one time only signal is used. The only other statefrom which an alarm may cause a transition is the RESET 10001 state.Thus ongoing communication is not disturbed and pending interrupts arenot issued until the master of the bus has issued a reset and isprepared to check for interrupts. This mode of issuing an interrupt isnot a one time only event and each time a reset is issued the modulewill enter the ALARM4 state 10101 until the interrupting source has beenreset.

Note that various applications of the modules will use theinterrupt/alarm capability during normal operation as discussed inconnection with applications in the following.

When a module is first connected to a host (perhaps along with othersimilar modules on a bus), and the host is quiescent (holding the nodeIO high), the module eventually goes into one of the reset states 00000and 10010, depending upon its previous condition, and waits for a lowsignal from the host. Note that in both of these states TPOSC isdisabled, so the state machine does not draw any current. Indeed,consideration of the inputs to latch 2208 shows that each of the threeinverted AND gates feeding the upper NOR gate corresponds to one of thereset states 10010, 10001, and 00000 to disable TPOSC. But a high nodeIO (as is the case for a disconnected module due to pull up transistorPULUP connected to node IO) will switch state machine from reset state10001 to state active state 10011, then after GT1 goes high to state00011 (presence detect signal), and next after GT5 goes high (300microseconds) to state 00001, and then to 00000 due to IO still high.Thus reset state 10001 can only be maintained by holding IO low. And aspreviously noted, while in state 00011 IOPULDWN is active to pull downterminal IO and generate the presence detect signal.

Overall Module Operation

As previously noted, the overall module operation follows a three layerhierarchical procedure: in the first layer the host sends a resetcommand by holding the IO node low for at least 480 microseconds andthen returning IO to high for at least 480 microseconds. This causesmodule to generate a presence detect signal by pulling node IO low forat least 60 microseconds as described in connection with FIG. 22F. Thereset command also clears the command register 2104 and sets the modulein a mode for the host to write a byte (8 bits) into command register2104 in the next eight write cycles as illustrated in FIGS. 2A-B anddescribed in connection with FIGS. 22B-E. Once command register 2104 isloaded with a command byte, command byte decoder 2106 decodes thecommand byte to initiate one of the four allowed commands: READ ROMDATA, MATCH ROM DATA, SEARCH ROM DATA, and SKIP ROM SECTION of thesecond layer. See FIG. 22G. (If the byte in command byte decoder 2106fails to match one of the available commands, then the module willsimply wait for a reset and ignore further commands at its inputs.)These commands employ identification data from the 64-bit ROM in 2108and incorporate the security aspects of the module. The upper portion ofFIG. 23A illustrates the flow. Successful execution of the second layercommand outputs a high at node PROT₋₋ OK to activate RAM 2110 which hasits own command register and decoding. The activated RAM 2110 reads thenext three bytes sent by the host into a three-byte command register.These third layer commands are available for access to the secure RAM2110. The lower portion of FIG. 23A shows the execution of these thirdlayer commands. Note that the flow paths all end in a reset. Also, thesecond layer commands dealing with the 64 bit ROM may have simplehardware support in that the entire 64 bits are read or compared so theaddressing can be simply incrementation and the successive comparisonsjust fed to a latch that switches if a mismatch occurs; see FIG. 22A.The following preferred embodiment discussions explain these commandsand variations in detail.

A preferred embodiment module 2300 has memory 2110 partitioned intothree secure and one nonsecure areas which provides functionality asfollows. The embodiment is a miniature security system that can storedata in three separate, secure memory areas (subkeys) or in ageneral-purpose scratchpad area. Each of the subkeys and the scratchmemory can be directly accessed. In addition, data can be written to thescratchpad memory, verified, and then loaded into one of the subkeys.Each subkey has an 8-byte ID field and 8-byte password associated withit; see FIG. 23B.

The module 2300 communicates over the 1-wire bus. Since the bus supportsmultiple modules, all bus elements have a unique 48-bit ID foridentification on the bus. The durable token package (FIGS. 1A-B) hasonly two electrical contact points, or faces, which makes this a ruggeddevice for use in harsh environments. A built-in battery maintains dataup to two years, or power can be drawn from the 1-wire bus.

The module 2300 is accessed via a single data line using the 1-Wireprotocol. The communication sequence, independent of the device, has twodistinct subsequences: the 1-Wire device selection sequence (secondlayer command) and the device-specific command sequence (third layercommand). The 1-Wire sequence precedes the device-specific commandsequence to identify the particular device on the bus.

Second Layer Commands

The 1-Wire protocol defines the System as a single bus master systemwith single or multiple slaves. In all instances, the module 2300 is aslave. The bus master is typically a microcontroller. The discussion ofthis protocol is broken down into two topics: hardware configuration andtransaction sequence.

The 1-Wire bus has only a single line, by definition; it is importantthat each device on the bus be able to drive it at the appropriate time.To facilitate this, each device attached to the 1-Wire bus must haveopen drain connections. The module 2300 is an open drain part with aninternal circuit equivalent to that shown in FIG. 23L. Ideally, the busmaster should also be open drain; but if this is not feasible, twostandard TTL pins can be tied together, one as an output and one as aninput. When using a bus master with an open drain port, the bus requiresa pull-up resistor at the master end of the bus. The system bus mastercircuit should be equivalent to the one shown in FIGS. 23M-23N. Thevalue of the pull-up resistor should be greater than 5K ohms. If thepull-up value is less, the bus may not be pulled to an adequately lowstate (<0.6 volts).

The idle state for the 1-Wire bus is high. If for any reason atransaction needs to be suspended, the bus MUST be left in the idlestate if the transaction is to resume. If this does not occur and thebus is left low for more than 480 microseconds, all components on thebus will be reset.

The protocol for accessing the memory of module 2300 is as follows:

Reset

Presence Detect

1-Wire Command Word (second layer command)

Device Command Word (third layer command)

Transaction/Data

CRC

All transactions on the 1-Wire bus begin with the reset sequence. Thereset sequence is started by holding the data line low for 480microseconds. The module 2300 is designed to be held in the reset statewhenever it is not connected to the bus. When it is connected to thebus, the data line is pulled high; the part is taken out of reset andthe part is ready to issue the presence detect.

After detecting a high state on the data line, the module 2300 waits 15microseconds minimum and issues its presence detect. This presencedetect is a low-going pulse that lasts 60-240 microseconds. Thisresponse to the reset pulse lets the bus master know that the module2300 is on the bus and is ready to operate. The presence detect helpsthe bus master to discriminate the communication signals from noise, asthe module 2300 is taken on and off the bus. Refer to the timing diagramin FIG. 23O. In a zero power standby condition the bus master can beidle and the presence detect signal used to wakeup the system.

After the module 2300 has responded to the reset pulse with a presencedetect, the bus master drives the bus to the idle state for a minimum of1 microsecond. This 1 microsecond interval is like a frame sync. Aftereach bit is transmitted on the bus, there is a frame strobe to sync upfor the next transmission. Refer to FIG. 23O.

Once the bus master has detected a presence, it can issue one of thefour different 1-Wire bus commands. Also, a fifth command to test abattery may be available; see the discussion in connection with thebattery test circuitry illustrated in FIG. 33. All 1-Wire commands are8-bits long and are loaded into the command register and decoded aspreviously described in connection with FIGS. 22A-H. A list of thesecommands is as follows:

CC (Hex) Pass Thru Mode

This command saves time by allowing direct access to the module 2300without identifying it by ROM ID number. This command can only be usedwhen there is a single slave on the bus. If more than one device ispresent, there will be bus contention.

33 Read ROM Data

This command allows the bus master to read the module 2300's unique48-bit ID number and CRC. This command can only be used if there is asingle module 2300 on the bus. If more than one is present, there willbe bus contention.

55 Match ROM Data

This mode allows the bus master to single out a specific module 2300 ona multidrop bus. The bus master selects the specific slave by the ROM IDnumber for the transaction. This command can be used with a single ormultiple devices on the bus; however, the specific ID of a desiredmodule must be a prior known by the bus master.

OF Search ROM Data

When a system is initially brought up, the bus master might not know thenumber or types of devices on the bus. By invoking the Search ROM Datacommand, the bus master can, by process of elimination, find the IDnumbers of all the devices on the bus. Once this is known, the busmaster can then go back and read the device type that corresponds toeach ID number.

ID SEARCH MODE

The ID search mode allows the host CPU to quickly compile a completelist of all the ID numbers of all the devices which are attached to acommon one-wire data bus. In this mode, each of the bits of the IDrequires three time slots of communication on the one-wire bus. Thefirst two time slots are read time slots in which the device transmitsback to the host CPU the value of the ID bit followed by its complement.The third time slot is a write time slot in which the host CPU suppliesits desired value for the bit. The device then compares the desiredvalue with the actual bit. If they disagree, the device waits for 480microseconds of continuous low (reset) on the bus and then reverts toits initial state. If they agree, the device increments its internalcounter to point to the next bit in the ID and then repeats the same setof three time slots for the next bit; see FIG. 23A. If all bits of theID are matched correctly during this process, the bus is coupledinternally to the underlying logic. After 480 microseconds of continuouslow on the bus, the device decouples the underlying logic and reverts toits initial state. If there is 480 microseconds of continuous low on thebus at any time during the ID search process, the device reverts to itsinitial state.

EXAMPLE OF ID SEARCH

The following example of the ID search process assumes four differentdevices connected to the same data line. The ID numbers of the fourdevices begin as shown below:

ID0: 00110101 . . .

ID1: 10101010 . . .

ID2: 11110101 . . .

ID3: 00010001 . . .

A complete search to identify these four devices is described below:

1. The host CPU begins by waiting 480 microseconds with the bus pulledlow, releasing the bus for another 480 microseconds, and then supplyingthe execution code to select the ID search mode.

2. The CPU executes two read time slots and receives two zero bits. Thisindicates that both one bits and zero bits exist as the first bit of theID's on the bus.

3. The CPU supplies a write zero time slot as the third slot in the setof three. This deselects ID1 and ID2 for the remainder of this searchpass, leaving only ID0 and ID3 coupled to the system.

4. The CPU executes two read time slots and receives a zero bit followedby a one bit. This indicates that all the devices still coupled (ID0 andID3) have zero as their second ID bit.

5. The CPU supplies a write zero time slot as the third time slot tokeep ID0 and ID3 coupled.

6. The CPU executes two read time slots and receives two zero bits. Thisindicates that both one bits and zero bits exist as the third bit of theID's of devices still coupled.

7. The CPU supplies a write zero time slot as the third bit. Thisdecouples ID0, leaving only ID3 still coupled.

8. The CPU reads the remainder of the ID bits for ID3 and communicatesto the underlying logic if desired. This completes the first ID searchpass, in which one of the ID's was found.

9. The CPU starts a new ID search sequence by repeating steps 1 through6.

10. The CPU supplies a write one time slot as the third bit rather thanthe write zero of step 7. This decouples ID3, leaving only ID0 stillcoupled.

11. The CPU reads the remainder of the ID bits for ID0 and communicatesto the underlying logic if desired. This completes the second ID searchpass, in which another of the ID's was found.

12. The CPU starts a new ID search by repeating steps 1 through 2.

13. The CPU supplies a write one time slot as the third slot in the setof three rather than a write zero as in step 3. This deselects ID0 andID3 for the remainder of this search pass, leaving only ID1 and ID2coupled to the system.

14. The CPU executes two read time slots and receives two zeros.

15. The CPU supplies a write zero time slot as the third bit. Thisdecouples ID2, leaving only ID1.

16. The CPU reads the remainder of the ID bits for ID1 and communicatesto the underlying logic if desired. This completes the third ID searchpass, in which another of the ID's was found.

17. The CPU starts a new ID search by repeating steps 12 through 14.

18. The CPU supplies a write one time slot as the third bit. Thisdecouples ID1, leaving only ID2.

19. The CPU reads the remainder of the ID bits for ID2 and communicatesto the underlying logic if desired. This completes the fourth ID searchpass, in which another of the ID's was found.

Note the following points with regard to the above example:

1. The host CPU learns the unique ID code of one device on each IDsearch operation. The time required to find each ID, assuming that nocommunication is performed to the underlying logic, is:

    960 microseconds+(8+3×64)×61 microseconds=13.16  milliseconds

The host CPU is therefore capable of identifying 75 device ID's persecond.

2. The data obtained from the two read time slots of each set of threehave the following interpretations:

a. 00: There are devices still coupled which have conflicting ID bits inthis position.

b. 01: All devices still coupled have zero in this bit position.

c. 10: All devices still coupled have one in this bit position.

d. 11: There are no devices still coupled. (This is an error condition.)

In the event that the logic of the connection between the variousdevices on the common bus is such as to wire-or the data instead ofwire-anding it, then the interpretations associated with 00 and 11 aboveare interchanged. (This might be the case for RF devices.)

All communications on the 1-Wire bus begin with the reset and presencedetect sequence. This sequence ensures the module 2300 is in thelistening mode. The bus master host CPU must then transmit the 1-Wirecommand to the module 2300. To transmit the first bit of the 1-Wire buscommand word, the master pulls the bus low for 1 microsecond. Thislow-going edge informs the module 2300 that the first bit is being sent.After 1 microsecond, the master does one of two things:

1) holds the line low for an additional 60 microseconds to output a 0(writes a zero) or

2) lets the bus go high for an additional 60 microseconds (writes aone).

The state of the bus during this 60 microsecond time phase determinesthe value of the bit. The module 2300 will sense any rising edge duringthis 60 microsecond time phase as a one. After the 60 microseconds havelapsed, the bus master must then drive the bus high for 1 microsecond.This is the frame sync mentioned earlier. This process is repeated untilall the 8 bits are transmitted. Refer to the timing diagram in FIGS.23P-23Q.

The bus master now reads the family code identifier, followed by thedata and a CRC. The read cycle is similar to the write cycle. It isstarted with the bus master pulling the bus low for 1 microsecond. Thisinforms the module 2300 that it should have data on the bus no laterthan the 1 microsecond from the falling edge. After the 1 microsecond,the bus master lets go of the bus and the module 2300 drives the bus.The slave must hold the data on the bus for an additional 14microseconds minimum (59 microseconds maximum). During the module 2300holding time, the bus master reads the state of the bus. Ideally, thebus master should read data from the bus 15 microseconds after thefalling edge. The entire cycle time for one bit lasts a minimum of 60microseconds (120 microseconds maximum) from the falling edge. At theend of the cycle, the bus master drives the bus high for 1 microsecond.Again, this is like a frame sync for the next bit. This read sequence isrepeated until all the data has been read. See the timing diagram inFIGS. 23R-23S for details. If for any reason the transaction needs to beterminated before all the data is read, the module 2300 must be reset.

To validate the transmitted data from the module 2300, the bus mastermay generate a CRC value from the data as it is received. This generatedvalue is compared to the value stored in the last eight bits of module2300. The bus master computes the CRC over the 8-bit family code and all48 ID number data bits, but NOT over the stored CRC value itself. If thetwo CRC values match, the transmission is error free.

Alternatively, the bus master computes the CRC over the 8-bit familycode, all 48 ID number data bits, and the stored CRC value. If the valueof the CRC value so computed is zero, then the transmission iserror-free.

An example of how to generate the CRC using assembly language softwareis shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        DO.sub.-- CRC:                                                                         PUSH    ACC         ;save the accumulator                                     PUSH    B           ;save the B register                                      PUSH    ACC         ;save bits to be shifted                                  MOV     B,#8        ;set shift = 8 bits                                                           ;                                                CRC.sub.-- LOOP:                                                                       XRL     A,CRC       ;calculate CRC                                            RRC     A           ;move it to the carry                                     MOV     ACRC        ;get the last CRC value                                   JNC     ZERO        ;skip if data = 0                                         XRL     A,#18H      ;update the CRC value                                                         ;                                                ZERO:    RRC     A           ;position the new CRC                                     MOV     CRC,A       ;store the new CRC                                        POP     ACC         ;get the remaining bits                                   RR      A           ;position the next bit                                    PUSH    ACC         ;save the remaining bits                                  DJNZ    B,CRC.sub.-- LOOP                                                                         ;repeat for eight bits                                    POP     ACC         ;clean up the stack                                       POP     B           ;restore the B register                                   POP     ACC         ;restore the accumulator                                  RET                                                                  ______________________________________                                    

This assembly language code is written for the DS5000 SoftMicrocontroller. The procedure DO₋₋ CRC calculates the cumulative CRC ofall the bytes passed to it in the accumulator. Note that the variableCRC needs to be initialized to zero before the procedure is executed.Each byte of the data is then placed in the accumulator and DO₋₋ CRC iscalled to update the CRC variable. After all the data has been passed toDO₋₋ CRC, the variable CRC will contain the result. The equivalentgenerating polynomial function of this software routine is:

    x.sup.4 +x.sup.3 +1

Third Layer Commands are initiated after the completion of a secondlayer command and signalled by the PROT₋₋ OK line going active toindicate that a valid second layer protocol has been satisfied.

Third Layer Commands

The module 2300 has six device-specific commands: Scratchpad Write,Scratchpad Read, Subkey Write, Subkey Read, Set Password and Move Block.This constrasts with the preferred embodiments having the four commandsillustrated at the bottom of FIG. 23A.

The module 2300 is controlled through a three-byte command word. Afterthe device is selected (by a second layer command), the command word iswritten into a register in memory 2110. The command word is comprised ofthree fields, each one byte long. The least significant byte is thefunction code field. This field defines the six commands that can beexecuted. The second byte is the address field. The first six bits ofthis field define the starting address of the command. The last two bitsof this field are the subkey address code. The third byte of the commandword is a complement of the second byte (FIG. 23C). Each command in thecommand word is address specific and therefore precludes the use ofcertain subkey codes and starting address locations (FIG. 23D).

Each of the subkeys within the module 2300 is accessed individually.Transactions to read and write data to a secured subkey start at theaddress defined in the command word and proceed until the device isreset or the end of the subkey is reached. The three commands thatoperate on the secure subkeys are Set Password, Secure Data Write, andSecure Data Read.

The Set Password command is used to enter the ID and password of theselected subkey. This command will erase all of the data stored in thesecure area as well as overwrite the ID and password fields with the newdata. The module 2300 has a built-in check to ensure that the propersubkey was selected. The sequence begins by reading the ID field of theselected subkey; the ID of the subkey to be changed is then returned. Ifthe ID's do not match, the sequence is terminated. The command sequenceis shown in FIG. 23E.

The Subkey Write command is used to enter data into the selected subkey.Since the subkeys are secure, the correct password is required to accessthem. The sequence begins by reading the ID field; the password is thenwritten back. If the password is incorrect, the transaction isterminated. Otherwise, the data following is written into the securearea. The starting address for the write sequence is specified in thecommand word. Data can be continuously written until the end of thesecure subkey is reached or until the module 2300 is reset. The commandsequence is shown in FIG. 23F.

The Subkey Read command is used to retrieve data from the selectedsubkey. Since the subkeys are secure, the correct password is requiredto access them. The sequence begins by reading the ID field; thepassword is then written back. If the password is incorrect, the module2300 will transmit random data. Otherwise, the data can be read from thesubkey. The starting address is specified in the command word. Data canbe continuously read until the end of the subkey is reached or until themodule 2300 is reset. The command sequence is shown in FIG. 23G.

The 64-byte read/write scratchpad of the module 2300 is notpassword-protected. The scratchpad can be used to store unsecured dataor it can be used to build up a data structure which can be verified andtransferred to a secure subkey. The three commands that operate on thescratchpad are Scratchpad Write, Scratchpad Read, and Move Block. Abuffered write capability is particularly invaluable in systems withnon-ideal communication links. In such a system without buffered writesthere is a distinct possibility of communication problems occurringconcurrent with updating of memory. This leads to the possibility of asupposed database consisting of partially old, partially new, andpartially garbage data. The write then verify then transfer capabilityis enabling for a sacrosanct database.

The Scratchpad Write command is used to enter data into the scratchpad.The starting address for the write sequence is specified in the commandword. Data can be continuously written until the end of the scratchpadis reached or until the module 2300 is reset. The command sequence isshown in FIG. 23H.

The Scratchpad read command is used to retrieve data from thescratchpad. The starting address is specified in the command word. Datacan be continuously read until the end of the scratchpad is reached oruntil the module 2300 is reset. The command sequence is shown in FIG.23I.

The Move Block command is used to transfer specified data blocks fromthe scratchpad to a selected subkey. This command might be used whendata verification is required before storage in a secure subkey. Datacan be transferred in single 8-byte blocks or a large 64-byte block.There are nine valid block selector codes that are used to specify whichblock is to be transferred (FIG. 23J). As a further precaution againstaccidental erasure of secure data, the 8-byte password of thedestination must be entered. If the password does not match, theoperation is terminated. After the block of data is transferred to thesecure subkey, the data in that block of the scratchpad is erased. Thecommand sequence is shown in FIG. 23K.

Application Modifications

Various applications make use of various capabilities of the module, andthe module may be modified or simplified accordingly. Indeed, modulesmay be used one at a time or many may be simultaneously attached to a1-wire bus; the module may be in the form of a coin-shaped token or maybe a traditionally packaged integrated circuit; the module may have aself-contained power supply (battery) or may tap power from the host ormay have a separate power supply input (which implies a third terminaland thus not easily adaptable to the coin-shaped package); and modulemay have a control or sense terminal (again a third terminal). TheSEARCH ROM DATA command permits identification of individual modulesamong many simultaneously attached to a 1-wire bus, but this commandwould not be needed if only one module were used and the READ ROM DATAwould suffice.

Some further applications for the module only use the identificationdata in ROM 2108 arid RAM 2110 finds no use. In such a case the modulecircuitry could be simiplified by omission of the RAM 2110 and itsattendant control circuitry. That is, only the upper center and lefthandportions of FIG. 23A would be used and after a successful bit matchthrough all 64 bits the module would output an indicative signal. Notethat if only a single module were to be used (such as for identificationon a printed circuit board with the module packaged in a standard TO-92plastic package and soldered to the board), then only the READ ROM DATAcommand may be needed and further simplify the circuitry. In such a casea further preferred embodiment module could be configured so that a hostor bus master microcontroller need not send a read command, but ratherafter reset such module is in a read mode. Contrarily, note thatmultiple identification-only modules could be simultaneously connectedto a bus so that the SEARCH ROM DATA command may be repeatedly used todetermine each of the identification numbers of the modules.

The following application modifications and variations of the module aidunderstanding of its characteristics and features.

Preferred embodiment module 2400 includes a ROM containing a 48-bitserial number, an 8-bit model number, and an 8-bit cyclic redundancycheck (CRC) byte. Module 2400 may be accessed to read its serial numberas noted in connection with the READ ROM DATA, and thus attaching module2400 to an item provides an identification tag for the item. Module 2400has only two terminals for connection with the outside world: ground andthe 1-wire bus connection IOPAD; the power for module may be a batterypackaged within module 2400 or may be drawn from the 1-wire bus througha diode so (as to not affect bus operation) and stored on a capacitor.Note that the preferred battery setup would be a 1.5 volt lithium orsilver oxide battery and low voltage CMOS FETs for the circuitry. Ifpower is drawn from the 1-wire bus, then a diode plus storage capacitorwith Zener diode voltage regulation could be used to power module 2400at any convenient voltage up to the 5 volts that the 1-wire bustypically is driven by high outputs of the bus master. Of course, ifmodule 2400 dissipates a large amount of power, then the bus master mustbe able to source large currents and the resistance of the bus must bekept low. A large number of low power dissipation modules can draw powerfrom a single 1-wire bus. FIG. 24A shows module 2400 in a TO-92 packageand mounted on printed circuit board (PCB) 2420; the ground terminal ofmodule 2400 simply connects to the ground bus on PCB 2420, and terminalIOPAD connects by 1-wire bus 2402 to an input/output pin ofmicrocontroller 2404 which is part of the array of integrated circuitson PCB 2420 and also to a probe point in the form of a plated throughhole 2406 in PCB 2420 as shown in detail in FIG. 24C. This use of module2400 provides an identification tag for PCB 2420 which may be read bymicrocontroller 2404 or by probe reader 2430 with probe 2432. FIG. 24Bshows the basic connection of module 2400 to microcontroller 2414without a probe point 2406 on PCB 2420. Module 2400 presents a highimpedance to the I/O pin of microcontrollers 2404 and 2414 except whenmodule 2400 applies a pull down. Thus module 2400 could be attached inparallel with other integrated circuits such as memories; the chipenable control of memories will keep them from contending with module2400. Microcontrollers 2420 and 2414 typically will have open collectorI/O pins when they are inactive, so 5K ohm pull up resistor R1 will holdan inactive I/O pin high. Of course, resistor R1 could be fabricated aspart of module 2400 and the third lead from the TO-92 package could beconnected to the power supply bus of PCB 2420. Additionally, the probepoint on PCB 2420 for contact with an external probe 2432 would permitan external reader 2430 to communicate with module 2400 even if PCB 2420is not powered up; external reader 2430 would pull up the 1-wire bus andsupply the power for a module 2400 that draws power from the 1-wire bus.

The probe point 2406 on PCB 2420 could be replaced by a two-pin headeraffixed to PCB 2420, and probe reader 2430 could just be a two-pinheader connector and plug directly into a personal computer or otherreading device.

Microcontrollers 2404 and 2414 read the 48-bit serial number, the 8-bitmodel number, and the 8-bit CRC byte from module 2400 as follows. First,the microcontroller resets module 2400 by pulling 1-wire bus 2402 or2414 low for at least 480 microseconds and then releasing bus 2402 or2414 to go high for at least another 480 microseconds. Module 2400recognizes the 480 microsecond low as a reset (see prior discussion) andin response resets its internal circuitry and provides a presence detectsignal (to inform the microcontroller of the existence of module 2400)by pulling the bus low for between 60 and 240 microseconds during the480 microsecond release by the microcontroller. See FIG. 22F which is atiming diagram. Note that the uncertainty in the duration of thepresence detect signal generated by module 2400 reflects the uncertaintyin the internal clock of module 2400.

After microcontroller 2404 or 2414 resets module 2400 and waits the 480microseconds with bus 2402 or 2412 released and detects the presencesignal of module 2400, it then serially writes the eight bits 0000 1111(0F in hexadecimal) forming the read command into the command registerof module 2400, one bit at a time, as previously described in connectionwith FIGS. 2A-B. The module clock period will be between 15 and 60microseconds so the set up time is taken enough less than 15microseconds to allow for the bus to be pulled high within 15microseconds if the microcontroller is to write a 0. Now the set up timebeing less than 15 microseconds implies that the start of the secondclock period after the initial pull down by the microcontroller will beduring a constant low or a constant high on the bus according to whethera 0 or a 1 is being written; the minimum clock period of 15 microsecondsmeans that the start of the second clock period is at 15 microsecondsafter the initial pull down and with the maximum clock period is at 60microseconds after the initial pull down. After each bit write, themicrocontroller releases the bus to return high, and then initiates thenext bit write by pulling the bus low for the set up time again. Module2400 recognizes each pulling of bus 2402 low as the beginning of a bitread or bit write or a reset and starts its internal clock, note thatthe reset is distinguishable because no pull down (new read or writebeginning) occurs for at least eight clock periods (480 microseconds isat least eight clock periods if a clock period is between 15 and 60microseconds).

Once the eight bits of the 1-wire command byte are written into thecommand register of module 2400, module 2400 recognizes the command byteand switches to read mode. Thus when microcontroller 2404 or 2414 nextpulls down bus 2402 or 2412 for the set up time, the response of module2400 is to immediately activate its pull down of the bus (which isalready low due to the microcontroller) and access its memory: if thebit at the current address in memory is a 0, then module 2400 continuesits pull down of the bus for the duration of a clock period (15 to 60microseconds), whereas if the bit at the current address in memory is a1, then module 2400 immediately release the bus. The microcontrollerthen reads the bit at the current address in module 2400's memory bysensing whether the bus stays low or returns high at the end of its pulldown for time period. Of course, the microcontroller must complete itssensing of the status of the bus prior to module 2400 terminating itspull down in the case of a 0 in memory. Again, after the bus hasreturned high, the microcontroller is able to initiate another bit readby pulling down the bus for the set up time, but to simplify the timingmicrocontroller will wait a full time slot prior to the next read; seeFIG. 3. The address counter in module 2400 increments each time themicrocontroller reads a bit, and the initial reset of module 2400 putsthe address counter a memory location 00. In this manner themicrocontroller can sequentially read all 64 bits in module 2400's ROMby supplying the pull downs to initiate the reads. After reading the8-bit model number and 48-bit serial number, the microcontroller cancompute the CRC value for these 56 bits and compare the result with the8-bit CRC byte read. If there is a disagreement in CRC values, then thereading process may be repeated, starting with the reset and commandwrite. A discrepancy in CRC values indicates a likely corruption of dataduring transmission. In short, the microcontroller or external reader2430 with probe 2432 can read the PCB identification number plus CRCcheck byte held in the ROM of module 2400 in a time of about480+480+8t_(SLOT) +64t_(SLOT) which is typically about 8.2 microsecondsfor t_(SLOT) taken to be about 100 microseconds.

The CRC byte stored in module 2400 ROM is computed from the serialnumber by the usual CRC algorithm using as generating polynomial x⁴ +x³+1.

Note that since only the contents of module 2400 are read, there is noneed of the flexibility of being able to write a read command to thecommand register of module 2400. Hence, a version of module 2400 withoutany command register and which just permits a host microcontroller toread its ROM contents after the reset (and presence detect, ifincorporated) has been completed.

Module 2400 may be attached to a PCB in other ways. FIG. 24D shows inplan view PCB 2440 which contains various integrated circuits 2450-2460(which may be items such as DRAMs, microcontrollers, and ASICs), module2400, and the board wiring with edge connector tabs 2470-2480. Personalcomputers typically have a number of boards analogous to board 2440 andwhich are inserted into connectors mounted on a chassis. Wiring amongconnectors and between connectors and ports provides theinterconnections of the various ICs and peripheral devices such asmonitors, keyboards, and printers. FIG. 24D shows module 2400 connectedbetween ground tab 2470 and tab 2473 which connects to a pin of aparallel port. Module 2400 may be in a small plastic package which willnot consume board space and usually can be soldered to the tabs withoutobstructing the insertion of PCB into a connnector. In other words,module 2400 may be attached to preexisting boards and does not need tobe designed in. Of course, a designed-in module would be more convenientand just take the place of serial number and other board identification.In any event, microcontroller . . . would probably only infrequentlyaccess module 2400, so speed of the reads and writes is not crucial inthis application. Furthermore, by putting a delay in the IO terminal ofmodule 2400 to prevent module 2400 from responding to short durationlows and incorporating the wait-for-reset state at the end of a ROM readwould permit attaching module 2400 directly to a port of amicrocontroller that is used for general purposes if long duration lowscan be ruled out. Or the reset for module 2400 could be extended torequire a long duration high following the long duration low.

Alternatively, module 2400 could be in the form of a coin-sized token2401 and inserted in a token receptacle 2491 mounted on PCB 2490; seeFIG. 24E which shows both plan and elevation views of token receptacle2491 with token 2401 indicating abutments 2492 that engage PCB 2490 andpins 2494 that extend into holes in PCB 2490 and are soldered to affixreceptacle 2491 to PCB 2490. A token 2401 form for module 2400 may be adisk on the order of 3 mm thick by 16 mm diameter. Thus a tokenreceptacle such as 2491 will take up more space on PCB 2490 than a TO-92package; but token 2401 is large enough to contain a battery and has theflexibility of allowing a change in the identification number of PCB2490 while still providing the serial number in ROM by just changingtokens.

Module 2400 on printed circuit board 2440 may also contain EPROM inplace of all or pan of the ROM and which can be programmed afterpackaging or possibly even after mounting on board 2440. This wouldpermit customization of the identification number held by module 2400.For example, if module has 48 bits of factory lasered ROM identificationand 16 bits of EPROM, then the full 64 bit identification is partiallyset electrically after packaging and to the requirements of thecustomer. FIG. 25 schematically illustrates circuitry for module 2400with EPROM bits in addition to the RAM plus lasered ROM memory. Module2400 includes a high voltage detector 2502; for a 5 volt CMOS module, a12-13 volt programming voltage usually suffices for FAMOS programming.The programming proceeds as follows. Following the satisfactorycompletion a valid second layer command as signalled by the PROT₋₋ OKsignal, either a read or write command of the program register isissued. This command consists of three bits of address to specify one ofeight bytes for writing, followed by five unused bits, followed by eightbits of data. First the address byte would be issued (LSB first):[A7-A0] only bits A0-A2 are significant to specify byte address andA3-A7 must be ones. Next follows the data bits (LSB first): [D7-D0] Eachbyte is buffered in an eight bit shift register which may be verifiedprior to providing the programming high voltage. If verify operation isnot desired than a 12V programming voltage of sufficient duration isimmediately applied and subsequently two bytes of new row addresses anddata can be shifted into the command register and the process repeated.This method accelerates programming speed for applications where thecommunication link is not suspect. Note that the device generatesseparate row and column high voltage signals and provides isolation oflow voltage circuits. A special single bit of EPROM may be written todisable subsequent writes to lock the EPROM with a known pattern. Thearchitecture of this EPROM is expandable and larger memories withincremental buffered write capabilities are possible.

Module 2400 may be powered by a direct connection to Vdd on board 2420or it may include an internal power source such as a battery or it maytap power from the one-wire bus with a diode plus storage capacitor.Module 2400 may also have a second diode plus storage capacitor for theprogramming high voltage. Of course, if module 2400 is in the form of atoken, then either the battery power or the tap from the one-wire busmust be used because only two terminals are available.

Module 2400 may be attached to the motherboard of a (personal) computer(either hardwired or as an inserted token) or to some other nodeaccessible by central microprocessor input/output, and theidentification contents within module 2400 can be checked in softwareprior to a program being run so that the program will not run if theidentification does not match a prescribed set of identifications.Indeed, a multiplicity of module token receptacles on a single boardcould be used, and software could have traps that permit execution ifany one of the modules has the proper identification. Alternatively, themodules with identifications for software users could be inserted to anexternal token receptacle device such as the parallel port plugextension 2600 schematically illustrated in FIGS. 26A-C and in copendingapplication Ser. No. 631,929, filed Dec. 19, 1990 (DSC-316) Indeed,parallel port plug extension 2600 includes spaces for five tokens 2602(one permanently affixed for plug extension 2600 identification and fourreplaceable for user tokens), Zener diode 2610, Schottky diodes 2620,and 1K ohm resistor 2630. Note that a personal computer typically usesthe parallel port for connection to a printer, and that plug extension2600 does not affect the printer operation because the printer strobeline remains high during the one-wire bus communication between host andtoken. Also, printer communications do not use line no. 13 although thisline and others were in the original IBM parallel port definition. Notealso that multiple plug extensions 2600 may be stacked to provide formore tokens 2602 on the same bus. If more than one module 2400 connectsto a one-wire bus, then further control logic as previously describedmust be included in the modules to allow the bus master controller todistinguish among the modules and read the identification of each oneseparately such as by the SEARCH ROM DATA command. Preferred embodimentmodule 2602 includes the identification capabilities of module 2400 andfurther provides for multiple modules on a single one-wire bus as inFIG. 26C. Note that the use of a unique identification number for eachmodule which is built in at the time of manufacture (48 bits impliesmore than 10¹⁴ different available identification numbers) plus thecapability of multiple (removable) modules on a single bus permits greatconvenience and compactness for applications such as softwareprotection.

A personal computer's parallel port pins may have EMI filters whichinclude capacitors that would stretch out rising edges and disrupt the1-wire signals to modules 2602. In such a case, the use of two parallelport pins with spaced falling edges feeding a NOR gate as in FIG. 26Dwill provide correct 1-wire signals.

READ ROM DATA for module 2602 is the same as the read command (0F Hex)for module 2400; that is, when bus master pulls the bus low each of themodules 2602 accesses the bit at the current address (which has beenreset to start at 00) of ROM and either pulls down the bus or releasesthe bus to indicate a 0 or 1 in ROM. And this is repeated to read outall 64 bits of ROM. Clearly this will not work to read ROM data if morethan one module 2602 is on the bus; but, in fact, it will bitwise givethe AND of the corresponding bits from the various modules on the bus.That is, the bus will be high only if all modules have a 1 bit, and thebus will be pulled low if any one of the modules 2602 has a 0 bit. Thusthe bus is a hardwired AND. Introducing an instruction to complement theROM contents before driving the pull down transistor of module 2602 willlikewise yield a bitwise hardwired NOR of the ROM contents. The READ ROMDATA command makes a module 2602 duplicate a module 2400, and a numberof modules 2400 on the bus will similarly bitwise read the ANDs of thecorrresonding bits of the ROMs.

MATCH ROM DATA puts module 2602 into a mode to compare its 64 bits inROM against 64 bits written by the bus master host; if a written bitagrees with the corresponding ROM bit, then module 2602 waits for thenext bit to be written; whereas, if a written bit disagrees with thecorresponding ROM bit, then module 2602 stops and remains inactive untila reset. Note that if the serial number is the only item of interest inthe module, then the MATCH ROM DATA command is typically not used.

SEARCH ROM DATA permits bus master to sequentially determine the ROMcontents of all modules 2602 on the bus as previously described. Indeed,if the bus master first attempts to read by using READ ROM DATA as if asingle module were on the bus, it will obtain the ANDs of the bits asdescribed above. Now the CRC algorithm will almost certainly indicate anerror. Hence, the bus master will try again and come up with the sameresult; so the bus master will, after receiving repeated read errors(the number depending upon the number of tries it makes to read),presume that more than one module 2602 is attached to the bus and changeapproach to Search ROM Data. Thus the bus master issues a reset for themodules and then loads Search ROM Data into the command registers of themodules. Then using the Search ROM Data routine, the bus mastergenerates a list of all identifications in modules on the bus, and thencan check whether a program should be run by comparison of this moduleidentification list with a list of permitted user identifications whichhave been inserted into the program.

Rather than use of a parallel port pin for the 1-wire bus as in FIGS.26A-C, other pins could be used for the 1-wire bus. For example, a1-wire bus could attach to a data/address line from amicroprocessor/microcontroller port to external memory because the linewill typically be held high except for short (less than 1 microsecondfor processor running at more than 1 MHz) low pulses during data readsand writes, and such pulses will not likely write any recognizable firstlevel command into a module. Indeed, anything written into the commandregister would probably be all 1's due to the usually high condition ofan address/data line. Further, such lines will not be low for 480microseconds to reset any modules except for power up situations. In apower up, if the processor avoids any memory communication for 480microseconds, then the presence detect signal provided by the modules onthe 1-wire bus will not cause any disruption. (Alternatively, a modulewhich does not emit a presence detect signal could be used.) Conversely,during communication with the modules, the chip enable signal from theprocessor to the memory will keep the memory inactive and the lows onthe address/data line will have no effect on the memory.

Similarly, a serial port could have an attached 1-wire bus, and hardwarehas been developed for this interface.

The typical use of an applications program by a personal computer userinvolves obtaining a copy of the program on a floppy disk, copying theprogram from the floppy disk to the hard disk of the user's personalcomputer, and then running the program using the hard disk copy. Theprogram typically consists of many files with the .EXE and .COMextension files the ones initially loaded and executing. If the personalcomputer has one or more modules 2602 on a bus connected to itsmicroprocessor (such as by the parallel port plug extension of FIG. 26Aor hardwired to the mother board as in FIG. 24C), then the ROMidentification can be used to limit execution of the program. Note theaddition of flange 2601 to modules 2602. A first approach, described inconnection with FIG. 27A, includes code in the program to access themodules and check identification. An alternative is to use a PROTECTprogram to reformat all of the hard disk files with .EXE or .COMextensions to incorporate a listing of all of the current ROMidentifications in these modules 2602 and to also incorporate a routinethat causes the microprocessor to SEARCH ROM DATA prior to any futureexecution and compare the found ROM identifications to the incorporatedlist and deny execution if none of the found ROM identifications matchesany of the incorporated identifications. This reformsting hard diskfiles for such identification protection permits both machineidentification (such as the affixed module in parallel port plugextension of FIG. 26A or the mother board hardwired module of FIG. 24C)to be incorporated into the .EXE and .COM files, but also useridentification by insenable modules (as the 2602 modules of FIG. 26A).Thus software manufacturers could provide an insertable module withidentification plus .EXE and .COM files which already have theidentification incorporated or which can only be executed one timewithout incorporated identification and during this execution theidentification of the module (or the machine's or the user's othermodules) is incorporated.

FIG. 27 illustrates a host computer 2702 which has a module accesssystem 2704 (which may be either software or firmware or a mixture) thatconnects computer 2702 to 1-wire bus 2706 with attached modules 2712,2714, . . . 2720. As in the previous examples, modules 2712, 2714, . . .2720 may be on a 1-wire bus that connects to the host at its parallelport as in FIGS. 26A-C, or on a bus attached to a memory address/dataline and located on a PC board, or to a contact on a keyboard. Note thatmodule access system 2704 is analogous to a network controller card in acomputer which is connected to a local area network. That is, accesssystem 2704 provides for computer 2702 to communicate with only a chosenone of the modules 2712, 2714, . . . 2720 on bus 2706. A preferredembodiment access system includes the following software functions:

Function SETUP (PN: Byte): Boolean;

This function must be called before any of the other functions toestablish the printer port number to be used and to perform timecalibration of the computer's machine cycle for a conversion to theapproximate 60 microsecond period of the modules' time periods. Thefunction returns True if 1<=PN <=3 and the printer port referenced by PNexists, otherwise it returns False. This function can be called at anytime to recalibrate timing and/or switch to a different printer port.

Function FIRST: Boolean;

This function returns False if SETUP has not yet been calledsuccessfully. If SETUP was successful, it issues a Reset signal andreturns False if no Presence pulse was detected. If a Presence pulse wasdetected, it performs the ROM search algorithm to find the first ROMdata pattern on the one-wire bus. It returns True if the search succeedsand False otherwise. The ROM data pattern that was found is stored in aninternal eight byte buffer.

Function NEXT: Boolean;

This function returns False if SETUP has not yet been calledsuccessfully. If SETUP was successful, it issues a Reset signal andreturns False if no Presence pulse was detected. If a Presence pulse wasdetected, it performs the ROM search algorithm to find the next ROM datapattern on the one-wire bus. It returns True if the search succeeds andFalse otherwise. The ROM data pattern that was found is stored in aninternal eight byte buffer. (The first time NEXT is called in a program,it is equivalent to the FIRST function. Before returning a False value,the code resets its internal pointers so that the following call to Nextis equivalent to a call to FIRST.)

Function ACCESS: Boolean;

This function returns False if SETUP has not yet been calledsuccessfully. If SETUP was successful, it issues a Reset signal andreturns False if no Presence pulse was detected. If a Presence pulse wasdetected, it transmits the ROM match command followed by the specificpattern in the internal eight byte buffer and returns True.

Function DATABYTE (X: Byte): Byte;

This function returns the value X if the function ACCESS has never beencalled or if the most recent call to ACCESS returned a False value.Otherwise, it transmits the byte X to the one-wire bus and returns thebyte received concurrently from the one-wire bus.

Function ROMDATA: Pointer;

This function returns a far pointer to the internal eight byte buffer.

Appendix A is a listing in assembly language for the Intel 8086, 80X86family of processors for the preceding access system functions. Theaccess system functions can be used as follows in a program to readsecure data from a module for authorization to execute a protectedprogram.

Found :=False;

LptNo :=1;

While not Found and SETUP(LptNo) do Begin

If FIRST then Repeat

KeyNo :=0;

While not Found and (KeyNo<3) and ACCESS do Begin <Use DATABYTE to readID from key number KeyNo>;

Found :=(ID=TargetlD);

If not Found then Inc(KeyNo);

End;

Until Found or not NEXT;

If not Found then Inc(LptNo);

End;

If Found then Begin

<Use DATABYTE to send the Password>;

<Use DATABYTE to read the Secure Data>;

<Execute the protected program>;

End else <Abort program because key not found>;

FIG. 28A shows preferred embodiment module 2800 which includes counter2810 in addition to converter 2802, command register 2804, decoder 2806,and ROM and control 2808, as in the module of FIG. 21. Indeed, module2800 roughly replaces the RAM 2110 of the module of FIG. 21 with counter2810. Module 2800 may be mounted on a PCB to keep track of the totaltime that PCB is active by using its internal clock to drive counter2810. Counter 2810 can be read over the 1-wire bus by a host in a mannersimilar to reading the RAM of module 2100: the host resets module 2800(counter 2810 does not reset except by a command in the commandregister), and then loads the Read Counter command into the commandregister and then reads the contents of counter 2810. Note that anestimate of the frequency of internal clock of module 2800 can simply bemade by reading counter 2810 at two times with a known time intervalbetween the reads. However, the accuracy of the internal clock may bemuch greater than that of the read timing, and this estimation would beunnecessary. Internal clock turns off if a low on the bus persists formore than 2 milliseconds and stays off (in reset idle state 00000) untilthe bus returns high. Thus if the PCB is powered down, and module 2800has a weak pull down of node IO, the bus will be low and internal clockwill stop without affecting the contents of the counter which is batterypowered. Thus the total powered up time of the PCB can be fairly easilyassessed by simply reading counter 2810; this permits a low costtracking of PCBs such as in mainframe computers where down time fromaging components can be deterred. An alternative embodiment could havetwo counters and a continuously running clock: one counter would againmeasure total powered-up time, and the second counter would measuretotal time to assess age. The following copending applications of commonassignee disclose subject matter related to module 2800 and are herebyincorporated by reference: Ser. No. 07/728,230, filed Jul. 10, 1991(pending DSC-317), Ser. No. 7/727,618, filed Jul. 10, 1991 (pendingDSC-319), Ser. No. 07/717,619, filed Jul. 10, 1991 (pending DSC-322),Ser. No. 07/727,638, filed Jul. 10, 1991 (pending DSC-324), Ser. No.08/103,724, filed Aug. 9, 1993 (pending DSC-352), Ser. No. 07/727,639,filed Jul. 10, 1991 (U.S. Pat. No. 5,297,099, issued Mar. 22, 1994),Ser. No. 07/728,229, filed Jul. 10, 1991 (pending DSC-354), Ser. No.07/727,270, filed Jul. 10, 1991 (pending DSC-355), and Ser. No.07/727,273, filed Jul. 10, 1991 (U.S. Pat. No. 5,166,545, issued Nov.24, 1992).

FIG. 28B schematically illustrates a temperature-controlledcounter/clock 2820 for preferred embodiment module 2800 in place ofcounter/clock 2810. The clock rate of counter/clock 2820 depends upontemperature, and counter/clock 2820 can thus measure thermalaccumulation and history. In particular, a chemical reactiontheoretically proceeds at a rate that depends upon temperature as √Texp(-E_(a) /RT) with T the absolute temperature, E_(a) the activationenergy per mole, and R the gas constant. Expressing the activationenergy in terms of energy per molecule yields the temperature dependenceform as √T exp(-E_(a) /kT) with k Boltzmann's constant. In practice theexponential dependence swamps the square root dependence, and atemperature dependence expressed by the exponential alone suffices andconstitutes Arrhenius's Law. Arrhenius's Law is the basis of thewell-known chemical rule of thumb which states that reaction ratesapproximately double for each 10 degree rise in temperature. Typicalvalues of the activation energy are roughly 50 to 100 kJ/mol or,equivalently, about 0.5 to 1.0 eV/molecule.

Counter/clock 2820 is a timer which measures chemical equivalent time,based on temperature according to Arrhenius's Law. Such a timer could beused to substantially extend the useful life of drug, enzyme, and otherchemical and biological stocks by providing the actual relevant thermalhistory instead of using a fixed lifetime specification based on theworst-case (i.e., highest) temperature. The same timer may also beuseful for indicating the freshness of food products. The timer would bea circuit in a token format module 2800, and token 2800 would just beplaced in proximity to the chemical or biological stocks of interest toinsure thermal equilibrium with the stocks. Then to take a lifetimemeasurement, either bring a host to read the token or carry the token toa host to read and then return the token to the stock proximity.

Counter/clock 2820 operates as follows. It is well-known that thecurrent through a semiconductor diode with a forward bias of V voltstheoretically depends on temperature by:

    I=C T.sup.3 exp(-E.sub.gap /kT)[exp(qV/kT)-1]

where C is a constant, T is the absolute temperature, E_(gap) is thebandgap of the semiconductor, q is the electronic charge in coulombs,and k is Boltzmann's constant. For diode biases of greater than 0.12volts and temperatures in the range of 0 to 100 degrees C the -1 termcan be ignored compared to the exp(qV/kT) term, so I depends on T as

T³ exp(-[E_(gap) -qV]/kT). As with the square root dependence forreaction rates, the cubic dependence is swamped by the exponentialdependence. Thus the diode current has the Arrhenius's Law form with theactivation energy equal to E_(gap) -qV. Silicon has a E_(gap) equal to1.12 volts, so with forward biases in the range of 0.12 to 0.62 voltsfor a silicon diode the current through the diode will emulate Arrheniusbehavior with an activation energy in the range of 50 to 100 kJ/mol. Theuse of a wide bandgap semiconductor, such as gallium arsenide, wouldprovide for emulation of higher activation energies, and the use of anarrow bandgap semiconductor, such germanium or InGaAs, would providefor lower activation energies.

Thus if the voltage across the diode is held at a constant value V, thenthe current through it will follow Arrhenius's Law. This provides ameans to exactly match the current equation to a specified chemistry, sothat the total charge flow (in coulombs) is exactly proportional to theelapsed chemical time (Arrhenius time). In counter/clock 2820 the diodeof interest is the base-emitter junction of npn transistor 2822, andbandgap generator 2824 generates a temperature independent outputvoltage V_(bg) which applies across the base-emitter junction. Thus thebase current and the collector current depend upon temperature accordingto Arrhenius's Law. Hence, converting the collector current to afrequency and using this frequency to drive counter 2840 will measurethe total charge flow and emulate Arrhenius time. For counter/clock 2820the current to frequency conversion arises from the collector currentpassing through p-channel FET 2826 which acts as a resistor and thevoltage drop across FET 2826 drives a voltage-to-frequency converter2830. The output of voltage-to-frequency converter 2830 drives counter2840. The dynamic range required of converter 2830 depends upon theactivation energy and temperature range involved; but very roughly, adoubling of the current for every 10 degree rise implies a converterdynamic range of about 1000 for a 100 degree temperature range. Forexample, a converter with a 1 mV to 1 V input range and an output of 10Hz to 10 KHz would suffice. Ultrawide-sweep multivibrators and chargebalancing converters can both meet such requirements.

Measurements of the temperature dependence (from 10 C to 80 C) of thecollector current through a particular silicon npn transistor withvarious voltages V applied across the base-emitter junction were fit tostraight lines of the Arrhenius form In(I)=ln(I_(o))-E_(g) /kT tocompute E_(a) as a function of V. Recall that theoretically E_(a)=E_(gap) -qV. The experimental results gave good fits to straight linesand yielded the following effective activation energies:

    ______________________________________                                               V     E.sub.a                                                          ______________________________________                                               0.3 V 0.91 eV                                                                 0.4 V 0.81 eV                                                                 0.5 V 0.71 eV                                                                 0.6 V 0.56 eV                                                                 0.7 V 0.44 eV                                                          ______________________________________                                    

This shows that a desired value of effective activation energy could beachieved by selecting an appropriate value of V to produce the desiredeffective band gap. As previously noted, chemical reactions typicallyhave activation energies in the range of 0.5 to 1.0 eV; so the siliconnpn transistor collector current can provide the appropriate temperaturedependence. Of course, for large activation energies, the transistorwill operate in a mode with small collector currents, and noise maybecome a limitation. Conversely, for small activation energies, thecollector current will be large and drain the battery plus generateheat. In this case intermittent operation would suffice: rather thancontinually monitoring the collector current, counter/clock 2820 couldjust turn on the bandgap generator and the npn for a few millisecondsevery ten seconds (or whatever time period would be appropriate forspeed of ambient temperature change) and thereby effectively sample thecollector current. The clock used to control the intermittent operationdoes not need to be accurate, as long as it's duty cycle remainsconstant. Note that the current gain of the npn transistor implies asmall current supplied by the bandgap generator supports a largecollector current supplied by the battery.

An alternative circuit used a thermistor to have the Arrheniustemperature dependence in the form of a changing resistance;experimentally the effective activation energy was 0.376 eV. Thethermistor was used as the R in an RC oscillator and the accumulatedcounts from the oscillator over small intervals of time were squaredbefore adding them to the Arrhenius time accumulator, then the effectivegap would be doubled to 0.752 eV, very nearly the desired value of 0.768eV for the "typical" reaction. In general, with a fixed (i.e., notvoltage-controlled) effective band gap, it is still possible to realizean exact match to the exponential coefficient in Arrhenius's Law bysampling the counts over small intervals and taking them to theappropriate power before summing them onto the Arrhenius timeaccumulator. This requires more computing power than the adjustableeffective gap method, since a mathmatical power must be computed eachtime a temperature measurement is taken. It might still be possible torealize this method with a dedicated special purpose microprocessorcircuit utilizing logarithm tables in ROM to accomplish the computationwith addition.

The following contains an analysis of the consequences of having anexponential coefficient in the Arrhenius time measuring device which isnot an exact match to that of the chemistry which is to be modelled.This mismatch may be due to imperfect calibration of the Arrheniusexponential coefficient in the device or to imperfect knowledge of thechemistry. It is shown that in the fight circumstances, a verysubstantial increase in useful shelf life can be realized even with apoorly calibrated instrument, although the largest increase is achievedwith the correct calibration.

Assume that a given chemical substance is required to be maintainedwithin the temperature range Tmin≦T≦Tmax, and that it has a specifieduseful shelf life based on Arrhenius's Law (with E_(a) /k abbreviated asTc) evaluated at the maximum temperature Truax:

Specified Lifetime=At^(*) exp(Tc/Tmax)

At another temperature T within the allowed range, the true useful shelflife of the substance is given by Arrhenius' Law:

True Lifetime=At^(*) exp(Tc/T)

The Arrhenius clock measures a useful shelf life given by:

Arrhenius Lifetime=Aa^(*) exp(Tg/T)

Let P=The percentage increase in the useful shelf life when theArrhenius Lifetime is used in place of the Specified Lifetime.

P=100^(*) (Arrhenius Life / Specified Life-1)

P=100^(*) [(Aa^(*) exp(Tg/T))/(At^(*) exp(Tc/Tmax))-1]

To calibrate the linear coefficient for the Arrhenius clock, we mustapply the condition that: Arrhenius Lifetime≦True Lifetime for allTmin≦T≦Tmax. This calibration condition divides into two distinct cases,depending on whether Tg≦Tc or Tg≧Tc, as follows:

Case A: Tg≧Tc (Arrhenius Life at Tmin=True Life at Tmin)

Aa^(*) exp(TgtTmin)=At^(*) exp(Tc/Tmin) (Cal. Cond.)

P=100^(*) {exp[Tc^(*) (1/Tmin-1/Tmax)-Tg^(*) (1/Tmin-1/T )]-1}for Tg≧Tc.

Case B: Tg≦Tc (Arrhenius Life at Tmax=True Life at Tmax)

Aa^(*) exp(Tg/Tmax)=At^(*) exp(Tc/Tmax) (Cal. Cond.)

P=100^(*) {exp [-Tg^(*) (1/Tmax-1/T)]-1}for Tg≦Tc.

These results show the following characteristics:

1. In Case A, if

T>Tg/[(Tg/Tmin)-(Tc/Tmin)+(Tc/Tmax)]

then the Arrhenius clock gives a lifetime that is less than thespecified lifetime. This is an undesirable result, indicating that Tg>Tcis not a good choice.

2. Case B produces an increase in lifetime for all temperatures in theallowed range (except Tmax, where the Arrhenius Lifetime is equal to theSpecified Lifetime)

3. In Case B, the lifetime extension is greatest when Tg=Tc. (The largerthe band gap, the greater the savings, provided that it doesn't exceedthat of the chemistry.)

4. The savings in Case B don't depend on the Arrhenius coefficient ofthe chemistry,Tc.

As a numerical example, suppose a "typical" chemistry (Tc=8912 deg) hasa specified storage range of 273.15 deg to 303.15 deg. What is themaximum P when measured with an Arrhenius clock based on our "typical"thermistor (Tg=4363 deg) with no correction for the disparity inexponential coefficients?

Pmax=100^(*) {exp[Tg^(*) (1T/min-1/Tmax)]-1}

Pmax=100^(*) {exp[4363^(*) (1/273.15-1/303.15)]-1}

Pmax=100^(*) (exp[1.58]-1}

Pmax=386%

What is the maximum P when measured with a band gap adjusted to matchthe chemistry (Tg=Tc=8912 deg)?

Pmax=100^(*) {exp[8912^(*) (1/273.15-1/303.15)]-1}

Pmax=100^(*) {exp[3.23]-1}

Pmax=2425%

While the exact match is clearly superior, the lifetime savings with thevery approximate match is still substantial.

Further embodiments of counter/clock 2820 include a programmable(whether EPROM or jtist in RAM) determination of the npn transistor biasV by storing bits that are feed to a digital-to-analog converter togenerate the bias V. Also, multiple npn transistors could be available,and the number used depend upon the bias; this will permit the totalcollector current (and thus counting rate) at a particular temperatureto be somewhat independent of the activation energy selected. Note thatat a V of about 0.5 volts, a change of 8 mV in the bias will result in a40% change in the current, and bandgap generators can maintain suchtolerances.

The module 2800 with the Arrhenius count/clock 2820 provides thefollowing features:

Miniature chemical freshness metering system sealed in a 16 mm microcan.

Self-powered with greater than ten years life from lithium battery.

Measures chemical equivalent time, based on temperature according toArrhenius' Law

Allows reading of the fraction of useful life remaining with a hand-heldreading device.

Allows reading of time during which the module was above (below) themaximum (minimum) temperature limits specified for a particular chemicalprocess.

Provides ROM containing a unique serial number for absoluteidentification and traceability.

Provides RAM to contain information about the chemical product that itis shipped with.

Provides RAM to contain factory calibration data so that the module cangive accurate measurements of Arrhenius time.

Can be programmed with the Arrhenius coefficients and limitingtemperatures for a specific chemistry with a hand-held programmingdevice.

Could be designed for one-time use to provide permanent short to ground(or short to internal battery) on expiration, to activate a simplecontinuity meter or an electrolytic color indicating overlay.

The Arrhenius time computation may also be packaged in containers otherthan that of module 2800 and may communicate by means other than that ofa 1-wire bus. Indeed, a package containing only the elements indicatedin FIG. 28B plus a liquid crystal display (LCD) to display the contentsof the counter would provide a Arrhenius time device totally independentof the 1-wire communications.

Preferred embodiment module 2900 includes features of modules 2400 and2602 but also provides a third terminal for control or sensing ofexternal events. FIG. 29A is a schematic block diagram of module 2900including a controlled switch, and FIG. 29B illustrates a distributedswitch and sensor application of modules 2900. In particular, FIG. 29Ashows that each module 2900 includes input/output terminal IOPAD,control logic and ROM analogous to that of modules 2400 and 2602 pluslatch 2902 and output CMOS inverter 2904 with a large (e.g., 1 Mohm)pull up resistor 2906 to switch/sense terminal SWOUT plus an interruptinput INT from terminal SWOUT. Current drain through pull up resistor2906 can be avoided simply by eliminating resistor 2906 and thep-channel transistor of inverter 2904, but this will limit applications.Use of the sense input leads to distributed address content keypads asillustrated in FIG. 29C where each SWOUT would be connected to apushbutton. Of course, FIG. 29B more generally shows a bus with amixture of modules 2900, some with control switches connected to SWOUTand some with sensors connected to SWOUT. Also, FIG. 29A specificallyshows a power supply that draws power from a 1-wire bus connected toIOPAD through a diode and stores it on capacitor 2910; this power supplyoption and the battery power supply option were already noted inconnection with module 2400. Of course, if the output SWOUT drives someother electrical devices, then there may be external power available;but if module 2900 is in a TO-92 package, then no fourth terminal existsfor a direct power supply for module 2900.

The distributed keypad of FIG. 29C can be used for various systems suchas a burglar alarm: each sensor connects to a window or door, and whenthe window or door is opened, the adjacent module senses this and setsan internal flag which enables the presence detect when reset by thehost. The host periodically (e.g., once a second) resets the modules andimmediately tracks down any received presence detect. FIG. 29D is a flowdiagram for such a system module. This system would also lend itself touse in a key pad scan input with wakeup as illustrated in FIG. 27E. FIG.29F illustrates such a system with the modules corresponding to itemsand keys on a cash register.

Alternatively, in the system of FIG. 29C the sensing of the window ordoor opening could generate an interrupt for the adjacent module, andthen, if the module were in reset idle state 00000, apply a pull down toIO for about 4 milliseconds followed by a usual presence detect, or, ifthe module were in an active state, when the host next sends a reset,the module responds with a pull down of IO for 4 milliseconds ratherthan the presence detect pull down. See the discussion in connectionwith state 00010 in FIG. 22E. After the interrupt pull down is released,the module performs its usual presence detect and switches into resetidle state 00000. In general, interrupts may be generated by modules ona 1-wire bus to request the host to read a status from the module orperform some other operation; this could be used in place of polling onthe sensor system. Various interrupt signals and timings are available;and each particular interrupt type may require special circuitry orgeneral purpose circuitry may be programmable to implement particularinterrupts. In particular, with a hardwired system as shown in FIGS.29B-C there is no worry about a spurious pull down of IO as could occurin a token system when a new token is added to the bus. Periodicsearches should be performed by the bus master to determine if anydevices have been removed from the system also indicating an alarmcondition (a disconnection of a sensor to circumvent the alarmsignalling).

Temperature sensing module has a preset temperature range which ifexceeded causes an interrupt request to the one-wire state machine. Amultitude of variously positioned and conditioned modules may be used tomonitor the temperature of a complex system through a single wire. Themodule contains an extremely low power real time clock and programmableperiodic internal signal which causes the temperature sensing circuitryto power up and perform a measurement. This relatively higher currenttemperature sensing circuit consists of a PTAT (proportional to absolutetemperature) voltage source and an A→D converter. The ability to use thelow power oscillator to periodically perform temperature measurementreduces the effective DC current by the duty cycle which can be threeorders of magnitude or more. This temperature sensor is configurablesuch that time/temperatures pairs are automatically stored innon-volatile memory so as to provide a time/temperature profile.

The distributed switch or sensor operation of module 2900 mimics that ofmodule 2300: the host may reset all modules 2900 on the bus by pullingthe bus low for at least 480 usec and then releasing the bus. Afteranother 480 usec (which includes the presence detect signals generatedby modules 2900), the host can load one of the commands Match ROM Dataor Search ROM Data into the command registers of all modulessimultaneously. As with module 2300 and explained in connection withFIG. 23 Match ROM Data and Search ROM Data have the host sequentiallysend bits to all modules 2900 on the bus and each module 2900 comparesthe received bit with its corresponding identification bit and decidesto continue if the bits match or to stop and wait for a reset if thebits mismatch; see flow diagram FIG. 23A. Of course, at most only onemodule 2900 will have 64 identification and CRC bits matching the 64sent by the host. If a module 2900 does match all 64 bits, then thismodule 2900 is the only module on the 1-wire bus that is not stopped andwaiting for a reset and it loads the next eight bits sent (in the usualwrite 0 or write 1 manner) by the host into its function register. Thefunction register contents are decoded to either turn on switchtransistor or leave it off or to respond to further bits sent by host todetermine turn on/turn off. With module 2900 in sensor functionoperation, the status of the pushbutton switch is sensed and eitherstored in a latch for host to read, or an interrupt is generated toinform the host of a particular status. Note that the sensing of thestatus of pushbutton switch can be on a periodic basis (such as roughlyonce a second) using the internal clock of module 2900.

FIGS. 30A-C illustrate a preferred embodiment system with module 2900which allows simple assembly of systems such as those shown in FIGS.29B-C. FIG. 30A shows the 1-wire bus as a twisted pair of wires3002-3003 with three couplers 3010 attached, each coupler 3010 includesa module 2900 with output stub wires 3022-3023 as shown schematically inFIG. 30B. FIG. 30C is a perspective view of coupler 3010 including snapon contacts which cut through the insulation on the twisted pair wires3002-3003 for electrical contact during assembly. Coupler 3010 measuresabout 10 mm by 5 mm by 5 mm and may be packaged in molded plastic foruse in harsh environments.

Another type of system uses modules 3100 similar to those of FIG. 29C,but with each module 3100 including a counter to keep track of thenumber of sensings. See FIG. 31A. The counters are read by the host on aperiodic basis, and the counters may be reset at each read. Such asystem could be used, for example, in a mouse for a graphic displaysystem; the mouse rollers will drive two sensors, one for each planardirection, and two modules for each sensor (one for increasing and onefor decreasing) will keep track of the distance moved by the mouse. Thiswould replace the current system of . . . The sensing pulses may come ata rate of one every millisecond, and the accuracy need not be high, sono special high speed counter is needed. See FIG. 31B.

A different type of one-wire bus device is shown in FIG. 32 and includesa digital potentiometer (the resistance between pin WIPER and pins HIGHand LOW can be adjusted by storing a setting byte in an internal wiperregister) which is configured so that a toggle switch (UP/DOWN) permitsincrementing or decrementing the wiper setting byte, and the contents ofthe wiper register can be read or loaded through the 1-wire terminaljust as with modules described above. Such a digital potentiometer canbe used for control of adjustments such as intensity, contrast, andvolume of televisions, computer monitors, and so forth. And if thecontents of the wiper registers are stored in nonvolatile memory, thenafter a power on (and self test), the stored contents for the wiperregisters can be loaded into the wiper registers with the identificationof the particular modules for the different adjustments selected withthe MATCH ROM DATA commands as previously described. In this manner,adjustments can be remembered.

A variety of three wire pans are available from Dallas Semiconductor aswell as other manufacturers, and an ability to communicate with severalof these devices through a single wire eases the system communicationrequirements. A system application could incorporate pairs of DS1267's(digital potentiometer) and a 1-3-wire converter requiring only groundand one other wire for communication. This would allow for example apiece of equipment such as an oscilloscope to have many independentcalibration adjustments performed through an external mono jackconnector. A one-to-three wire bidirectional transceiver enables thisoperation and could be based on converter 2102 by coupling the DATA₋₋ INand DATA₋₋ OUT to a single mode. The second layer commands and register2104, decode 2106, and ROM and control 2108 could also be pan of aone-to-three wire transceiver; see FIG. 37A. A possible implementationof this transceiver would require a great deal of additional circuitryand signals to control the data direction (i.e. whether thebidirectional D/Q port was configured as an input or an output). In apreferred embodiment the need for such additional circuitry is obviatedby a passive determination of data direction. This is accomplished bywriting a resistive high logic 1 and relying on the 3-wire part tooverdrive this to a zero if a read 0 was indicated; see FIG. 37B.

FIG. 33 schematically shows test circuitry 3300 that may be included inmodules 2400, 2602, . . . to permit testing of an on board battery or abattery embedded within a module and hence inaccessible for voltagelevel and thereby determine the expected remaining useful batterylifetime. Test circuitry 3300 includes node IO connected to the IOPADterminal, nodes BATTESTB and RSTINT as inputs to latch 3302, flip-flop3304, comparator 3306 with positive input node P and negative input nodeN, input buffer 3308 including a Schmitt trigger and RC filter, inverterwith hysteresis 3310 and output pulldown n-channel transistor PULDWN.Comparator 3306 has positive input node P connected to the bus at nodeIO and negative input node N connected to the battery and output nodeOUT feeding inverter 3310 which then drives output pulldown transistorPULDWN through inverters 3312. Test circuitry 3300 operates with ananalog tester host controlling and sensing the 1-wire bus as follows:The tester host first resets all modules on the bus; then the testerhost sequentially writes the 8-bit command Battery Test into the commandregister of the modules as previously described, and then the testerhost sequentially writes 64 identification bits which the module matchesbitwise as described for the Match ROM Data command to select out aparticular module for battery testing. The selected module then enterstest mode by driving BATTEST low which switches latch 3302 to clockflip-flop 3304 to J=1 and thereby activate comparator 3306 and K=0 toactivate inverter with hysteresis 3310. The tester host has so far beenoperating as the typical host by using 5 volt highs; but now the testerhost drops the voltage to about 1.7 volts because the battery voltage isin the range of about 1.55 volts down to about 1.0 (lower than 1.0 voltand module is inoperable). Next, the tester host begins slowlydecreasing the voltage on the bus in increments of 25 mV with eachincrement of duration about 100 microseconds. When the voltage on thebus reaches the battery voltage, comparator 3306 switches from an OUThigh to OUT low and this turns on pull down transistor PULDWN and pullsthe bus low which the tester host senses and thus determines the batteryvoltage as the last voltage applied to the bus prior to it being pulleddown by the selected module. After holding the bus low for roughly 50nanoseconds, the selected module releases the bus by driving RSTINT highto reset flip-flop 3304 to J=0 to inactivate comparator 3306 and K=1which inactivates inverter with hysteresis 3310 and turns off pull downtransistor PULDWN and also returns BATYESTB high. Note that if thebattery voltage is very low, then the tester host . . . will have thevoltage on the bus going low which will cause input buffer 3308 toswitch from high to low and reset flip-flop 3304 if RSTINT is still low;this prevents inadvertent battery drain.

FIG. 34A shows host 3401 and modules 3402-3403 which communicate over aradio frequency or infrared band in place of the one wire bus. Thediscussion will be in terms of radio frequency (RF) communication. Host3401 has associated transmitter TX1 and receiver RX1, and modules3402-3403 have associated transmitters TX2 and TX3 and receivers RX2 andRX3. The transmitters are drawn to broadcast an RF signal upon a highinput, and the receivers are drawn to output a high while receiving anRF signal. Only a single RF transmission band is used becausetransmitted and received data are time-multiplexed on the same band,analogous to the half-duplex signals on a one wire bus. A frequency ofof at least 1 MHz is used and this is sufficient to demodulate the 8microsecond time domain signals required.

The NOR gates and wave shapers coupling the transmitters and receiversto the host and modules insure that a transmitter and receiver for asingle device never operate at the same time and also provide delaysthat account for system speed limitation to allow possiblecommunication, so the transmitter and receiver could be designed as atransceiver and thus share much of the same analog circuitry. Note thatthe wave shapers (the inverter string 3410 plus NOR gate 3412 andinverter 3414) provides for a short delay for a rising edge and a longerdelay on a falling edge due to the inverter string. The delay times canbe set by RC time constants, delay lines, inverter propagation as inFIG. 34A, or other devices. The transmitter-receiver fully supports thecapabilities of the one wire bus as previously described, and no RFtransmission occurs during idle, so power (and battery life) isconserved. Note that the NOR gates plus transmitter and receiverarrangement is the same for host 3401 and modules 3402-3403, so a commontransceiver design could be used for both. A low on a one wire buscorresponds to transmission and reception in the RF band, and that ahigh on a one wire bus corresponds to no transmission in the RF band.When host 3401 or a module 3402-3403 is outputting a low and itsreceiver is not receiving, then the inputs to the NOR gate to thetransmitter are both low and the transmitter is activated. But then thehigh output of this NOR gate holds the NOR gate from the receiver loweven if the receiver begins to receive a signal. Once host 3401 or amodule 3402-3403 outputs a high, then the NOR gate to the transmittergoes low and turns off the transmitter plus releases the NOR gate fromthe receiver to allow reception to pass to the host or module.

FIG. 34B is a timing diagram for the reads and writes over the RF band.Note that most of the transmissions come from host 3401 which typicallywill have a standard power supply and not be relying upon batteries asdo modules 3402-3403.

The RF band in place of a hardwired one wire bus permits use of modulesin token form or other form for applications such as security badges, .. . where physical contact would be awkward or inconvenient. The formfor an RF module could be a token as in FIGS. 1A-B with one face made ofmetal (RF ground plane) and one face made of plastic and having anopening for connection from the internal elements to a spiral arminductor running from the opening outward and acting as the antenna. SeeFIG. 34C for a perspective view. Preferably the antenna operates wellbelow its lowest resonant frequency. If it is desired to lower theantenna's lowest self-resonant frequency (to increase RF coupling), thespiral inductor can be extended out onto the cylindrical portion of thetoken (made of plastic) and be capacitively loaded by the metal RFground plane face. Contrarily, if it is desired to raise the resonantfrequency, then the inductor can be configured as a multiarm spiral, orcan be less tightly wrapped. If it is desired to lower the Q of theantenna, the spiral can be made of narrower metal or can be taperedtowards its end. Further, a ferrite may be placed in proximity to theantenna to increase its effective RF cross section.

The RF module could also use non-resonant RF transmission techniqueswith a direct driving of signal edges onto a radiating structure toachieve a small-amplitude transmission. With such a transmission scheme,time domain relationships can be used to achieve processor gain. In thefrequency domain, such a transmission would appear as a weak broad-bandsignal; however, the processing gain of such signals can be analyzedusing orthogonal basis function sets other than transcendentalfunctions, as is often done in analysis of spread-spectrumcommunications. Indeed, in spread-spectrum techniques a message to betransmitted is involved with a very long binary sequence, and theresulting signal is used to modulate a RF transmitter. The resulting RFsignal can be transmitted with very low spectral power density (so lowthat a receiver which does not have at least some information about thebinary sequence may be unable even to detect that a transmission isbeing made) and still be accurately received by the intended receiver,which uses the same binary sequence for decoding.

Note that there is no problem of cross-talk if the transceiver transmitand receive links operate at different frequencies. A two frequencyapproach however requires that two different receiver/transmitter linksbe available thereby complicating the implementation. The RF transceiveris essentially an inverting transceiver and thus demonstrates theduality of the `wired or` and `wired and` operation of the link. Whereasthe open drain one-wire operates in a `wired and` mode, if the halfduplex RF communication in air is considered as the one wire link it isclear that if any device is signalling the receiver will detect this andthus a "wired or" operation is apparent. Nonetheless the "search"algorithm is possible and uniquely identifies multiple devices in thefield and isolates conversation to individual devices. Note that othernon-resonant mode electromagnetic communication methods are possible.These methods may incorporate close range inductive coupling by whichthe master may induce a signal which is demodulated with a non-linearelement followed by a low pass filter (envelope detection) in order toprovide the correct time domain electrical signals to the device. Inorder to read the one-wire device requires the ability to sense whetherthe n-channel MOS device is on which normally pulls the one-wireelectrical line low. This is accomplished by measuring the energydelivered to the transmitting inductor since the energy absorbed by thecoupled inductor is greater if the MOS device is on than off. A secondapproach utilizes two transmit frequencies and couples these to thepickup coil. If the MOS device is on the non-linearity of the diode ismanifested through mixing terms which are not otherwise present and thusthese are in turn coupled back to the transmit coil where bandpassfiltering and envelope detection is employed for sensing a one or zero.These standard RF techniques allow the `touch` devices to becomeproximity devices capable of contactless communication.

FIGS. 35A-B are cross sectional elevation views of a pushbutton token inwhich the mechanical switching action implies that the moving piece 100Cis electrically connected to shell 100A (through contact 2116) when themoving piece has been depressed as shown in FIG. 35B. A dome-shapedspring 2110 with a hole in the center to permit passage of contact 2116is coated with an insulator (or placed on an insulating washer, notshown) so that it does not make electrical contact to the moving piece100C. A teflon sleeve 2112 insulates the sliding contact between piece100C and shell 100B and also provides some dirt exclusion. Spring 2110provides some mechanical hystersis to help debounce the contact. Theheight of contact 2116 is selected to provide the desired degree oftravel and resistance. If sleeving 2112 is dimensioned for a tight fit,air resistance will add to the effective force of spring 2110; whereas,if sleeving 2112 is dimensioned for a somewhat looser fit, airturbulence will add a damping force to the switch's action.

In pushbutton token structures the substrate is preferably used toprovide two contacts: a fixed protrusion from the substrate whichextends up through ring-shaped insulator 2114, locates the token, andmakes contact to the bottom shell 100B; another contact is positioned tobe contacted by moving piece 100C when it is depressed as shown in FIG.35B. The simplest way to implement this is with a substrate whichincludes a dense array of token-receiving sites: each token would haveto be placed on a token-receiving site, but a wide variety of resultingconfigurations could be achieved.

FIG. 35C shows a simple, handheld token reader in cross sectional view.

FIG. 36 is a schematic circuit diagram of repeater 3600 for use with aone wire bus. Long busses present a large capacitive load to the hostand modules on the bus, and these devices may have insufficient power toprovide short rise and fall times for signals. Inserting one or morerepeaters 3600 into a bus with the bus connected to the I/O terminals ofrepeater 3600 will lessen the load seen by the host or modules. Repeater3600 operates as follows. When the bus is in an inactive high, NOR gateswith hystersis 3602-3603 are both low and pull down transistors 3612 and3613 are both off. Now if a device connected to the portion of the busconnected to I/O terminal 3622 pulls that portion of the bus low, thenNOR gate 3602 will have two low inputs and switch to a high output. Thehigh from NOR gate 3602 turns on transistor 3612 and pulls down I/Oterminal 3623 and thus drives the portion of the bus connected to I/Oterminal 3623 low. The high from NOR gate 3602 also drives wave shapingcircuit 3607 to input a high to NOR gate 3603 after a delay of about 200nanoseconds which is less than the time it takes node 3634 to go low.Thus NOR gate 3603 has one high input and one low input or two highinputs during this switching, although the inputs switch, and thehystersis of NOR gate 3603 insures that it remains with a low output.Thus transistor 3613 remains off. Then when the portion of the busconnected to I/O terminal 3622 is released and goes high, NOR gate 3602switches low and turns off transistor 3612 and provides a low input towave shaper 3607 which delays this low about 200 nanoseconds to NOR gate3603. Resistor 3633 connected to a power supply then pulls the portionof the bus connected to I/O terminal 3623 high in less time than thedelay of wave shaper 3607. NOR gate 3603 again has one input high andone input low that switch, and the delay of wave shaper 3607 and the NORgate's hystersis holds it in the low output state. Hence, the portion ofthe bus connected to I/O 3623 follows a low signal on the portion of thebus connected to I/O terminal 3622. For a device active on the portionof the bus connected to I/O terminal 3623 the operation of repeater 3600is symmetrical and the portion of the bus connected to I/O terminal 3622will follow a low.

Rather than providing a one wire bus, possibly with repeaters, the hostand modules of the foregoing embodiments could tap off of an existingbus which has a fully defined bus architecture, such as a VME bus.Indeed, in a bus which includes a serial bus portion, the D/Q line canbe used as a one-wire bus whenever the CLK and RST lines are inactive.

Numerous applications of tokens as convenient, secure informationcarriers exist: the National Bureau of Standards has promulgated a DataEncrytion Standard (DES). A token could contain one 64 bit key and bereadable by a computer which also does the decoding of a publishedencoded message, or the 64 bit key could be read out of a module andinto a dedicated DES Processor such as the DS2160 as manufactured byDallas Semiconductor Corp. Similarly, a token could contain a generatorpolynomial for a spread-spectrum binary sequence to decodespread-spectrum transmissions. This could be adapted for pay-per-view TVbroadcasts.

Further Modifications and Variations

It will be recognized by those skilled in the art that the conceptsdisclosed in the present application can be applied in a wide variety ofcontexts. Moreover, the preferred implementation can be modified in atremendous variety of ways. Accordingly, it should be understood thatthe modifications and variations suggested below and above are merelyillustrative. These examples may help to show some of the scope of theinventive concepts, but these examples do not nearly exhaust the fullscope of variations in the disclosed novel concepts.

For example, by including integrated circuits with more securityfeatures (such as a DS1207 TimeKey™ from Dallas SemiconductorCorporation), the module bus architecture can also be used forapplications where security is a high priority. Advantageousapplications of this type may include "smart cards", personnelidentification badges, and electronically verified currency.

For example, the RAM/ROM hybrid cell of FIG. 11 could alternatively beimplemented with EPROM-type transistors. In this case, the combinationof fuse 1130 and transistor 1140 would be replaced by a singlefloating-gate transistor. For another example, the laser-blown fuses1130 used in the presently preferred embodiment of FIG. 11 could bereplaced by electrically-blown fuses instead.

For another example, many advantages can be obtained by adapting thedisclosed concepts to a module which included electrically programmableelements (EEPROM memory or EEPAL logic) instead of battery-backed memoryand logic. Such a module would be more expensive, and would require amodified bus protocol (so that the module could be powered from the dataline while in contact with the host).

For another example, the board in the module of FIG. 11 can be flexibleor rigid, and can be made of conventional or other printed-circuit-boardconstruction. Similarly, the one or more integrated circuits in themodule can be packaged in a SOIC or other conventional package, ormounted using chip-on-board or chip-on-flex techniques, or mounted inother ways, as long as sufficient hermeticity is achieved. (Preferablythe packaging technique is also selected to minimize cost.)

For another example, the system and method disclosed for interfacing anelectronic token to an RS232 port can be applied to serial ports usingother standards. Even without exploiting the capabilities of UART chips,tokens can be interfaced to a very wide variety of serial ports, or toports such as pins of the parallel printer port on a standard PC.

The contents of the data field in the module can be chosen by thesystems designer, and a wide variety of formats can be used. Of course,some additional software would normally be used on the host side forData Error Checking. For example, cyclic redundancy check bits may beencoded with the stored data, using a variety of methods.

Of course, a much more accurate time base in the module can be providedby using a higher battery voltage. However, the use of the low batteryvoltage of the presently preferred embodiment is advantageous inproviding low cost and low power consumption. It should be noted that(in line with the discussion above regarding FIGS. 5A and 5B) that amore accurate time base could also be achieved by modifying the CMOSprocessing to lower the transistors' threshold voltages V_(TP) andV_(TN). However, as is well known to those skilled in the art of CMOSdesign, such a modification would carry its own costs (e.g. increasedsubthreshold current), and therefore is not presently preferred.However, it is important to note that some of the advantages of some ofthe disclosed innovations could be realized in such an environment.

It must be understood that the many teachings set forth herein can beused separately. For example, a symmetric two-sided token package couldbe used instead, with a contact in the center of each face. This wouldnot be as cheap nor as robust as the package of FIG. 1A, but many of theteachings could be adapted for use in such an embodiment. Symmetry canalso be achieved with the previously described embodiments by readingwith a reader with two signal lines, with the "data" and "ground"functions of these two lines periodically interchanged.

For another example, the charge consumption due to precharge of columnswhich are not being read during a memory access could be reduced byconfiguring the memory as multiple subarrays. (This might beparticularly advantageous when using larger memory sizes.)

An additional second layer command is possible available only forinterrupt capable devices. This command is similar to "SEARCH" but onlydevices with active interrupts respond. This command enables amulti-drop system to be quickly polled to determine the source ofinterrupts.

For another example, the packaging of the module can be widely varied,even within the context of a module which interfaces to a one-wire bus.For example, it is contemplated that a standard connector configuration(such as a subminiature 3/32" phone plug) could be used to define pinplacement for a data module. While such configurations are believed tobe as advantageous as the principal preferred package embodiments, suchalternative package embodiments do have their own advantages, and manythe teachings set forth herein can be used in such a context.

As will be recognized by those skilled in the art, the conceptsdescribed in the present application can be modified and varied over atremendous range of applications, and accordingly their scope is notlimited except by the allowed claims.

What is claimed is:
 1. A communication module comprising:(a) asubstantially token-shaped body with first and second electricallyconductive surface areas and having a perimeter around saidsubstantially token-shaped body, said first and second electricallyconductive surface areas electrically isolated from each other, saidfirst and second electrically conductive surface areas forming a cavity,one of said first or second electrically conductive surface areasforming a flange that extends substantially around said perimeter ofsaid substantially token-shaped body, said flange extending outward andaway from said substantially token-shaped body, said flange residing inone geometric plane; (b) circuitry positioned in said cavity within saidsubstantially token-shaped body, said circuitry electrically coupled tosaid first and second electrically conductive surface areas; (c) whereinsaid circuitry provides receipt of and transmission of digital signalsas voltage differences between said first and second electricallyconductive surface areas; (d) wherein said first electrically conductivesurface area comprises a first flat face of said substantiallytoken-shaped body; and (e) said second electrically conductive surfacearea comprises a second flat face parallel to said first flat face and acurved surface which is perpendicular to said first flat face and saidsecond flat face, said second flat face forming said flange.
 2. Acommunication module comprising:(a) a substantially token-shaped bodywith first and second electrically conductive surface areas and having aperimeter around said substantially token-shaped body, said first andsecond electrically conductive surface areas electrically isolated fromeach other, said first and second electrically conductive surface areasforming a substantial portion of said substantially token-shaped body,said first and second electrically conductive surface areas forming acavity, one of said first or second electrically conductive surfaceareas forming a flange that extends substantially around said perimeterof said substantially token-shaped body, said flange extending outwardand away from said substantially token-shaped body, said flange residingin one geometric plane; (b) circuitry positioned in said cavity withinsaid substantially token-shaped body, said circuitry electricallycoupled to said first and second electrically conductive surface areas;(c) wherein said circuitry provides receipt of and transmission ofdigital signals as voltage differences between said first and secondelectrically conductive surface areas; (d) wherein a portion of saidcircuitry is a small outline integrated circuit having a plurality ofpins electrically coupled to a printed circuit board, said printedcircuit board positioned in said cavity, said small outline integratedcircuit electrically coupled via said plurality of pins and said printedcircuit board to an energy source from a voltage intermittently appliedbetween said first and second electrically conductive surface areas,said energy source also positioned in said cavity; and (e) wherein saidfirst electrically conductive surface area comprises a first flat faceof said substantially token-shaped body and said second electricallyconductive area comprises a second flat face parallel to said first flatface and a curved surface which is perpendicular to said first flat faceand said second flat face, said second flat face forming said flange,and said flange extending entirely around said perimeter.
 3. Thecommunication module of claim 2, wherein said first flat face iscircular in shape and has a diameter of approximately 16 mm.
 4. Acommunication module comprising:(a) a substantially token-shaped bodywith first and second electrically conductive surface areas and having aperimeter around said substantially token-shaped body, said first andsecond electrically conductive surface areas electrically isolated fromeach other, said first and second electrically conductive surface areasforming a substantial portion of said substantially token-shaped body,said first and second electrically conductive surface areas forming acavity, one of said first or second electrically conductive surfaceareas forming a flange that extends substantially around said perimeterof said substantially token-shaped body, said flange extending outwardand away from said substantially token-shaped body, said flange residingin one geometric plane; (b) circuitry positioned in said cavity withinsaid substantially token-shaped body, said circuitry electricallycoupled to said first and said second electrically conductive surfaceareas; and (c) wherein said circuitry provides receipt of andtransmission of digital signals as voltage differences between saidfirst and second electrically conductive surface areas; (d) wherein aportion of said circuitry is a small outline integrated circuit having aplurality of pins electrically coupled to a printed circuit board, saidprinted circuit board positioned in said cavity, said small outlineintegrated circuit electrically coupled via said plurality of pins andsaid printed circuit board to an energy source for storing energy from avoltage intermittently applied between said first and secondelectrically conductive surface areas, said energy source alsopositioned in said cavity; and (e) wherein said plurality of pins equalseight.
 5. The communication module of claim 2, wherein saidsubstantially token-shaped body is button-shaped.